Apparent competition between vegetative phase and fruiting phase

Carbohydrate to Nitrogen Ratio

(This appears to be the nucleus of a unifying model of floral induction. It unites photoperiodism, shading, girdling, temperature variations, humidity, and other conditions on the basis of their effect on the carbohydrate:nitrogen ratio. Root-bound plants, for example, would be expected to receive less nitrogen, relative to their potential for photosynthesis. Girdling and binding would trap carbohydrates above, while allowing nitrogen to move upwards from the roots. Scapes or stems removed from a plant would receive no more nitrogen from the roots, while retaining their carbohydrates. In other words, any condition—external or internal—that affects the carbohydrate:nitrogen ratio could influencing flowering and fruiting.)

Roberts (1927)
How do very poorly vegetative trees become strongly vegetative by being placed in a short photoperiod? The change in percentage of nitrogen appears directly related to the fall in specific gravity due to a reduced carbohydrate content. With the respiration of carbohydrate material there is a corresponding liberation of available nitrogen, as NIGHTINGALE (3) has found in the tomato. If carbohydrate respiration is a liberator of nitrogen forms which make for increased growth then carbohydrate accumulation must have previously been a binder of those nitrogen forms. Does carbohydrate accumulation inhibit vegetative extension? Do accumulating reserves check growth as well as accumulate after growth in length is checked? That could be an interpretation of the reduced growth of girdled trees. Girdling so changes other factors that this evidence might be weak. The relation of amount of elongation to composition in the shade-and-girdling series does, however, appear suggestive. The probable, if not apparent, relation of carbohydrate accumulation to reduced growth has many practical applications in connection with such questions as dwarfness, period of growth, ''old age" in trees, partial etiolation, the rest period, as well as with blossom bud formation.

Roberts & Struckmeyer (1948)
Poinsettia plants in short days, but too warm at night to initiate blossom, can also be brought into blossom by wrapping taut rubber bands about the stems near the tips. When blossoming is induced in this manner, characteristic changes in the anatomical structure were found to occur above the point of banding.

Sterility and Gigantism

Knight: Upon the effects of very high temperature on some species of plants (1819)
The Melon. Plants of this species were trained upon a trellis near the glass, which was of the best quality, and these exhibited a greater degree of health and luxuriance, than I had ever before seen; but not a single flower ever unfolded; a great profusion of minute blossoms, nevertheless, appeared in succession at the points of the shoots, all of which perished abortively. I was much disappointed at the result of this experiment; from which I confidently expected to obtain fruit of the greatest excellence.
The Water Melon. A plant of this species, treated in the same manner as the melon plants above mentioned, grew with equal health and luxuriance, and afforded a most abundant blossom; but all its flowers were male. This result did not, in any degree, surprise me; for I had many years previously succeeded, by long continued very low temperature, in making cucumber plants produce female flowers only; and I entertain but little doubt, that the same fruit-stalks might be made, in this and the preceding species, to support either male or female flowers, in obedience to external causes.

Cook: Suppressed and Intensified Characters in Cotton Hybrids (1909)
Many plantings of Central American varieties of cotton in Texas have been rendered completely sterile through the exclusive development of vegetative branches from the axillary buds instead of fruiting branches, which arise from extra-axillary buds. This behavior may be viewed as an intensification of the vegetative tendency, which remains largely in abeyance when the plants develop in a normal manner, as they are able to do after a few seasons of acclimatization, that is, if the first plantings do not carry the vegetative intensification to the point of complete sterility.

Cook: Cuzco Corn (1916)
The usual behavior of the Cuzco corn in the United States is to produce plants of enormous size that mature very little seed, often none at all. It has been taken for granted that the size of the plants should be in proportion to the enormous kernels, and that our seasons were not long enough to permit this type of corn to mature.
     But in Peru one does not see these gigantic, infertile plants, nor any indication that the corn crop requires a large amount of heat to bring it to maturity. The impression one gets from the Peruvian corn-fields is that the plants are not taller than with us and rather more slender, the most striking peculiarity being the prevailing red color of the foliage. The best development and largest ears of the Cuzco corn are found in some of the higher valleys, at elevations between 9,000 and 11,000 feet, in districts where the summer climate is cooler than in any of the corn-growing regions of the United States.

Karpechenko: The production of Polyploid Gametes in Hybrids (1927)
Dominance of biennial over annual habit

Burbank: Methods and Discoveries 6:68 (1914)
Still greater interest attaches, perhaps, to hybridizing experiment in which the parents were Shaffer's Colossal raspberry and the Crystal White blackberry.
     Some of the plants from this cross were of the most tree-like proportions. Most of them, however, were barren, though they bloomed freely. But there were exceptional ones that fruited, and selected seedlings were grown from these through a series of generations. In the fourth generation a plant appeared which was of such extraordinary characteristics that it was given the name of Paradox.
     This plant was in all respects a most perfect combination of the two ancestral forms from which it sprang. The wood, bark, leaves, blossoms, prickles, roots, and seeds could not by any test be proved to be like one or the other. The fruit, produced in abundance, was an oval, light red berry of good size, larger than that of either progenitor, and of fair quality.
     Many of the first generation descendants of the Paradox were partially barren, though blooming freely. Sterility as to fruit was often associated with gigantic growth.

Separating stems from plants

Neil O. Anderson, Breeding and Genetics (2007)
Most hybridizing in private and public sector breeding programs has been conducted in greenhouse conditions. Viehmeyer and Uhlinger (1955) developed a ‘water culture’ method to accommodate situations of limited greenhouse space. This technique was accidentally discovered after chrysanthemum stems cut for use as pollen sources were allowed to senesce in a vase and produced seeds. In 1951, the water culture method was re-tested with cut stems placed in jars of water, in lab conditions (ambient temperatures and light conditions), and proved successful in seed production. Subsequent trials demonstrated that seed could be ripened in darkness, seed viability and % seed set were equal to in situ ripening, and seed maturation occurred 2-4 wks. earlier (Viehmeyer and Ulhlinger, 1955).

B: New Varieties of Potatoes from Seeds (1846)
In autumn, soon after the appearance of the first heavy frosts, let the potato balls or apples be gathered, macerated in water, the seeds separated from the pulp, and placed in some convenient place in the shade, to dry; after which they may be packed up in an air-tight box or bottle, and kept until required for use. As few of the early sorts produce blossoms, in order to produce seeds from them, deprive the plant of its tubers as they appear, and keep the runners from which they proceed above ground, by not earthing up the plant, and blossoms and seeds will soon appear.

Knight: On raising new and early Varieties of the Potato (1820)
Having fixed strong stakes in the ground, I raised the mould in a heap round their bases, and in contact with them: on their south sides I planted the Potatoes from which I wished to obtain seeds. When the young plants were about four inches high, they were secured to the stakes with shreds and nails, and the mould was then washed away, by a strong current of water, from the bases of their stems, so that the fibrous roots only, of the plants, entered into the soil. The fibrous roots of the Potatoe are perfectly distinct organs from the runners, which give existence, and subsequently convey nutriment, to the tuberous roots; and as the runners spring from the stems only of the plants, which are, in the mode of culture I have described, placed wholly out of the soil, the formation of tuberous roots is easily prevented; and whenever this is done, numerous blossoms will soon appear, and almost every blossom will afford fruit and seeds.

Beaton (1861)
Mr. Knight made an experiment for getting early Potatoes to seed by planting them on a ridge, and when the plants were ready to bloom he washed away the soil of the ridge to prevent them making young tubers, and so force the whole strength of the plants or roots into the stems and foliage to see if that would force them to seed. Another form of that experiment is applicable to all bulbs and tubers which form roots on the flowering-stems, as the Japan Lilies and others do. Pot such bulbs or tubers with the neck of the bulbs just at the surface, and when the stem is an inch or two put an empty pot over it, introducing the stem through the hole at the bottom of the pot, then earth up the stem, and when it roots and fills the upper pot separate from the bulbs, then cross it.

Beer: Seed Production of Cut Flowers (1897)
Referring again to the complete sterility of Amaryllis reginae, under ordinary conditions, he adds that "scarcely, however, have we separated the inflorescence from its root, and laid it aside without moisture, than it forms large seed capsules, and clearly shows us that these would always be produced if the vigorous root formation did not rob them of all nourishment."

Traub: Artificial Reversal of Growth Dominance in Amaryllids (1935)
In a large number of trials, self or cross pollinated flowers of excised amaryllid scapes, especially those of Hippeastrum, placed in water or nutrient solution, have in the great majority of cases produced seeds. Within limits, the number of seeds per capsule seems to be largely a function of the relative size ("fleshiness") of the peduncle

Caldwell: At Long Last—Seeds On Lycoris squamigera (1979)
So in the flowering season of 1976 I went back to work on L. squamigera, using pollen from L. sanguinea, L. sprengeri, L. chinensis, L. "Sperryi" and from a new unidentified yellow lycoris that looks much like L. squamigera. Reciprocal crosses were made. I cut about 40 scapes, labeled them and hung them in light shade in my greenhouse. For a time they made progress; seed capsules fattened in an encouraging way. However, in September when they were fully ripened it was a disappointing task to shell out the capsules, umbel after umbel, and find no seed. But one scape looked particularly good and, sure enough, when I peeled away the capsule covering, there they were—three large, shiny, hard black seeds, one of them fully 3/8" in diameter. This may sound absurd but plant breeders will understand—it was like finding gold nuggets after a 20-year search!

Allen: Experiment's on Mr. Pell's Farm (1845)
The grain was cut when the straw presented a yellow appearance four inches above the ground. At that stage of its growth, a milky substance could be expressed readily from the kernels, by gentle pressure of the forefinger and thumb. It was allowed to remain three days on the field, when it was carried to the barn and threshed out immediately. It weighed 64 lbs. per bushel, and sold for 12 1/2 cents above the market price by weight. A few acres were left standing, and cut three weeks after, when others in the neighborhood harvested their wheat. This proved small, shrivelled, and weighed 56 lbs. per bushel. The straw had lost its most nutritious substances, was much lighter than that cut earlier, and was consequently less valuable. Mr. Pell thinks that after the stem turns yellow near the ground (there being no connection between the root and the tassel), the kernel wastes daily. By early cutting, nearly all the saccharine matter is preserved in the straw, and it is thus rendered almost as valuable for fodder as hay.

Whyte: Relationships of Developmental Physiology (1960)
For maximum production of grains in an annual cereal, growth processes are allowed to proceed to their end, until such time as the developmental processes and building of the grain exercise a completely inhibitive effect upon growth and the plant bearing the ripe fruit dies. Where optimal environmental conditions are available for fruiting, the straw is of little value, everything having been supplied to the grain. Where conditions are below the optimum, grain yields are lower and ripening more difficult, but the straw is of higher nutritive value for livestock. Growth has continued longer owing to the lower inhibitory effect of the development, and less building material is supplied to the grain.
     The striking of an appropriate balance between growth and reproduction is the basis of good management of grassland for grazing or hay production.

Russell: Proliferous Character of the flower-salk of the Lilium Candidum (1835)
...the flower-stalk of the White Lily (Lilium Candidum), cut immediately after the sepals have fallen, and kept in an upright position in a cool and shady situation, will evolve from the axis of its bracteal leaves distinct bulbs, capable of producing perfect plants. My attention was first attracted to this curious fact by the kindness of a friend, some three or four years since, and I have uniformly been successful in the result, whenever I have renewed the experiment. But the vital energy is not only continued and developed in the production of these hitherto adventitious bulbs, several of the capsules even ripened sound and vigorous seed.


Nicolas: Sterility encountered in rose breeding (1927)
Paul's Scarlet Climber as an own root plant may be considered as sterile, but a grafted plant will bear both self- and hand-pollinated seeds.

Van Fleet: Rose-Breeding Notes for 1918 (1919)
Owing to its poor seeding abilities when grown as grafted plants on heavy soil, less progress has been made than was hoped for with R. Moyesii, notable among wild roses for the deep red coloring and waxy texture of its widely expanded blooms. Now that our plants have been transferred to the sandy loam of Bell Experiment Plot, and have become established on their own roots, seeds are more freely borne, and a fair number of hybrids are under way. Pollen was plentifully produced, even when the fruits failed to mature, and a few early crosses, the result of applying it to the stigmas of other species and varieties, have sufficiently developed to show prospective value.

Jacobs: Padre of the Roses (1937)
Father Schoener undertook many experiments with those native flowers, but his initial attempts at hybridizing and domesticating them were disheartening. He chose the hardy wild Nutkana as a parent stock because it could withstand the cold northern climate and it bloomed early. He selected the Paul Neyton [sic], an old and large French rose, as its mate. Working literally like a bee, he pollenized 1,500 blooms the first spring. But the only result was to prove what he had learned in his botany classes: that a wild rose will not take pollen from any other species.
    Then his next step was to graft the Nutkana onto the vine of the Paul Neyton as a sort of blood transfusion. It worked! –and after fertilizing this plant, he obtained five perfect fruits. The product of this seed is Schoener's Nutkana, well known to rose lovers — a large, single pink rose, which sends up shoots seven to eight feet high each year and produces bunches of flowers from every eye along the stem.

Meehan: Budded Roses (1855)
Every body knows why a Pear is grafted on the Quince. The Quince is naturally a shrub, ten or fifteen feet in height, and of the same natural family of plants as the Pear, which will "take," or bud or graft, freely on it; but in so doing, loses its tendency to become a tree, and while thus assimilating in size to the Quince, gains an additional power to flower and bear fruit. This is in accordance with the physiological doctrine, that what tends to check the wood-forming principle of vegetation, increases its power to blossom and bear. The Rose can be, and is, budded for the same reason, though not for that reason alone.

Davis: Malnutrition and segregation in Oenothera (1921)

  1. Harvests of seed from selfed plants in the F1 generation of reciprocal crosses between brevistylis and Lamarckiana were collected by the middle of August; these gave F2 generations from seed ripened under normal conditions. Following the collection of the first harvests the F1 plants were again selfed and then all of the leaves and side branches were removed so that second harvests of seed were ripened under experimental conditions of malnutrition; these gave F2 generations from seed ripened under conditions of malnutrition (table 1). The F2 cultures then grouped themselves in pairs, a normal and an experimental culture having the same F1 parent plant. All cultures were grown from seed forced to complete germination.
  2. The experimental cultures (from seed developed under condition of malnutrition) showed uniformly a smaller percentage of brevistylis segregates, and there were such extreme ratios as 1:17, 1:10.5, 1:7.4, 1:5.4, etc., when the ratios in the normal cultures were close to 1:3. These lower ratios of brevistylis in the experimental cultures following malnutrition of seed were consistently correlated with lower percentages of germination (one exception), and with the presence in the experimental cultures of large numbers of abortive seedlings, called "stumpy" because a root failed to develop from the tip of the hypocotyl. This is the evidence for the writer's view that malnutrition of developing seeds in the F1 generation of this material lowers the ratio of brevistylis segregates in the F2 by increasing the mortality of brevistylis zygotes or embryos.

Altered Conditions, Transplanting, Starving, Infection and Drought

Downing: The Van Mons Theory (1849)
It will be remembered that it is a leading feature in this theory that, in order to improve the fruit, we must subdue or enfeeble the original coarse luxuriance of the tree. Keeping this in mind, Dr. Van Mons always gathers his fruit before fully ripe, and allows them to rot before planting the seeds, in order to refine or render less wild and harsh the next generation. In transplanting the young seedlings into quarters to bear, he cuts off the tap root, and he annually shortens the leading and side branches, besides planting them only a few feet apart. All this lessens the vigor of the trees, and produces an impression upon the nature of the seeds which will be produced by their first fruit; and, in order to continue in full force the progressive variation, he allows his seedlings to bear on their own roots.

Genesee Farmer, 24(2): 88 (February, 1863)
The Balsam, or Lady Slipper, is well known. It has been greatly improved, and the flowers are now frequently as large and double as the rose. They should be transplanted once or twice, so as to check the growth of leaves, and favor the development of the flowers.

Burbank: Fragaria californica (1914)
We have seen that plums and many other plants are stimulated to exceptional growth by precisely such a change. But when the promising wildlings from the Yosemite were transplanted to my gardens they ran to vines and produced very little fruit, although in their native habitat they had borne abundantly.

Sorauer (1895) quoted by Wiggans 1918, Mo. Agr. Exp. Sta. Research Bul. 32
Of our apple trees it is a well known fact that in warm insular climates they grow into magnificent foliate trees but remain unproductive of fruit.

Shomel: Corn Culure and Breeding. 51st Annual Report of the Indiana State Board of Agriculture XLIII (1901-1902).
In most seasons, cowpeas and soy beans, drilled between the rows of corn just after the last cultivation, give good results. These crops will produce from one to two and one-half tons of hay per acre and will increase the fertility of the soil. Where the soil is a rich prairie loam the soy bean is more successful than the cowpea. On such rich soils the cowpea runs to vines and does not mature a seed crop.

Herbert (Amaryllidaceae) (1837) - Camellias
p 367: The reason that the seedlings raised by some nurserymen are so very inferior is, that their plants are in the most luxuriant growth; and it cannot be expected that seed gathered from individuals growing with freedom and vigour, should not be more disposed to reproduce the natural form of the plant, than to yield the fine cultivated varieties, which are to be obtained from them when almost diseased by repletion.
p 370: Having cultivated the myrtle-leaved above twenty-five years, I never saw that variety bear an anther in my collection, except one season, when all the flowers on every plant of the kind had them, and they were found in two or three late flowers last year; but the seedlings reared from its pollen, of which great expectations were entertained, proved to be the worst I had ever raised, and it seemed that whatever peculiarity of the season inclined the flowers to deviate from their usual double form, and approach nearer to the fertile single-flowered original, disposed also the pollen to generate single seedlings. I have seen the myrtle-leaved with anthers at Mr. Knight's nursery, though the circumstance has been so rare in my own collection; perhaps it may be connected with the more or less luxuriant growth of the plant.

Prof. Blake: Proc. Soc. Hort. Sci. (1911)
I think from certain observations that the peach is perhaps more susceptible than the apple to differences of fertilizer treatment and other conditions. In the experiments in New Jersey, it has been quite noticeable that sometimes a check to the trees, such as attacks of scale, results in very large fruit. During the past two or three years some winter injury has occurred, and those trees which have not been too severely injured produced very large specimens, even though there was a very large crop on the tree.

Prof. Drinkard: Proc. Soc. Hort. Sci. (1911)
Reed, at the Virginia Station, has reported a case where a blight of some kind had caused the blooming of certain trees in the fall of the year, and he attributed the premature blooming to the influence of the blight. There is no doubt that the cessation of vegetative growth has a marked influence on fruit-bud formation, but to what extent they are correlated I cannot say.

Nicolas: Rose Infections (1933)
Summer defoliation is not always due to disease, although diseases will precipitate it. Summer defoliation did not bother our fathers before the introduction of Austrian Briar blood. Austrian Briars will lose their foliage early because it matures early. It is the nature of the beast that nothing can change, and all their hybrids inherit that character in a greater or lesser degree. When the foliage is mature, the "cortex" or film of corky material that heals the pores where the leaf is attached to the branch begins to form, the leaf receives less and less nutrition from the plant and drops at the least provocation, spray or dust notwithstanding.
[This may relate to the apparent sterility of R. foetida. If the plant is not allowed to go dormant (usually being "forced" to grow by a foreign rootstock), it may compete with the fruiting phase — drawing back nutrients needed to ripen fruit and seed. Would girdling help?]

American Agriculturist, 2(6): 179 (1843) by S. S.
The writer visited an amateur strawberry gentleman this spring, who had various kinds. His Hovey bed was taken peculiar care of, so that he could present his friends some. The writer asked him if they had borne well? He replied they were very large—he would find him one; after some little time, one was found, very large, and if strawberries were raised, to be looked at, or taken in small quantities, like medicine, then under the present treatment, they would answer. The runners of these vines in the garden referred to, were four feet long. Mr. Longworth says a plant in his garden, in one year, covered with runners three square feet of ground. Now no plant can do both; make a large amount of stems, foliage, and runners, and bear fruit or berries at the same time.


Popenoe: Origin of the Banana (1914)
Seeds may be produced in an ordinarily sterile variety as a result of environmental conditions, if there is any basis of fact in the story given to O. W. Barrett by a Porto Rican native, who advised: "Get a stool of bananas growing rapidly in shallow soil by the addition of artificial fertilizers; let one bunch of fruits set; but before that ripens, cut down all but one of the stems in the clump. The remaining shoot, 'thinking it has but one more chance to perpetuate its kind before being killed,' on account of the tremendous shock to the more or less connected stem bases in the clump, at once produces a small bunch of somewhat abnormal fruits, some of which will contain seeds."

Schulz: Hardgrove Shock Treatment (1954)
As soon as the flower stalk begins to wilt it is cut off; also cut off all the leaves except the very small center ones. Lift the amaryllis from the pot and cut back the roots to about two inches. Then repot in fresh soil and set the plant in a shady place until the leaves begin to lengthen. At this point, you can put it back with your other amaryllis, if you wish, and it will very likely show another bloom stalk.


The Avocado, a Salad Fruit from the Tropics, USDA B.P.I. Bull. 77. p. 31-32 (1905)
G N Collins
Extension of season is an important desideratum, especially in the direction of later fruiting forms, the desirability of which is considered farther on. Advance in this direction is likely to be made by the introduction of new varieties and, perhaps, by extending the cultivation of the trees to regions of more continuous moisture where the season of flowering can be to some extent controlled. The tree flourishes in many localities where it fails to bear fruit, and, as with the mango, this sterility is usually found in localities of almost continuous humidity. Under such conditions an artificial check, such as root pruning, has been found to induce flowering and the setting of fruit. This can easily be overdone, however, in which case the trees will bear one large crop and then die.
     Some of the most prolific trees are those grown in rather small depressions of porous rock in southern Florida, where the plants are, in a manner, root-bound, while the porous nature of the rock affords good drainage. There are a number of ways in which the growth may be checked and the yield increased. The baring of the roots to the sun would appear a very satisfactory method. A custom of hacking the trees to make them bear is practiced by the Indians of Mexico. In any case where the fruiting is induced by artificial means the season will be more or less under control.

The Mango in Porto Rico, USDA B.P.I Bull. 28. (1903)
G N Collins
The mango will grow in a variety of conditions, and it seems to have little preference as to soil, the most important requirement being a deep soil that is well drained. As to climate, it is much more exacting, and the fact that the tree may thrive in a given locality and yet fail to produce fruit should always be kept in mind. It may be considered as proven that the mango will be prolific only in regions subjected to a considerable dry season. On the moist north side of Porto Rico the trees grow luxuriantly, but they are not nearly so prolific nor is the fruit of such good quality as on the dry south side, and in the very dry region about Yauco and at Cabo Rojo the fruit seemed at its best, while its abundance was attested by the fact that fine fruit was selling as low as 12 for a cent. In Guatemala and Mexico the mango was found at its best only in regions where severe dry seasons prevailed.

Seminar on Research & Development of Fruit Trees (1980)
Mangoes show generally good growth and production throughout Jamaica. The problem areas include Manchester and the North coastal areas including some areas of St. Ann. In some of these areas, the mango achieves good vegetative growth, but fruiting is poor and at best biennial or less regular. (Mathias — personal communication), pointed out that the variety Ann, grows well on the marl soils of St. Ann's Bay, with good fruiting and fruit characteristics. The variety when transferred to Lima in St. James, however, did not reproduce those same fruit qualities etc. The mango can grow well on a wide range of soil types and needs a long dry period for flowering and fruit set. The occurrence of heavy rainfall and strong winds during this period will reduce mango yields drastically.

Atmospheric Pressure

High atmospheric pressure and fruit trees (1929)
I V Michurin
In some years, in the latter part of August, there is a long period of constant high atmospheric pressure (between 760 and 770 mm.). This, according to my observations, greatly affects the organisms of perennial plants and forces some of them to bloom again in the autumn.
     In such cases, certain varieties of apple, cherry, mountain ash, bird cherry, and others have a second budding.
     In such years a second flow of sap is also observed in hybrid seedlings, and against which we cannot take any measures; but in selecting we must not reject such damaged hybrids as lacking hardiness.

Science 2(27): 178 (August 10, 1883)
Influence of diminished atmospheric pressure on the growth of plants.—Experiments conducted by Wieler at Tübingen show, that, all other external conditions being the same, plants will grow more rapidly under diminished atmospheric pressure. Thus, if a specimen of the common Windsor bean (Vicia faba) be grown in a receptacle in which the pressure of the air can be controlled, it will be found to grow faster until the pressure has been diminished to 100-300 mm.; the normal pressure under which the ancestors of the plant have flourished being, of course, not far from 760 mm. If, however, the pressure is reduced below the smaller figure given above, the rate of growth diminishes. Wieler found that the curve of growth of the sunflower is about the same as that of the bean. It was further shown by his experiments, that growth is retarded by increased puressure until the minimum is reached at 2-2 1/2 atmospheres, from which point there is again an increase. Although the short abstract of these interesting results so far published is meagre in the extreme, it indicates that the field entered upon by Wieler (and by Bert in France) may compel us to revise some notions now held in regard to the adaptation of plants to their surroundings in past ages, and at the present time upon high mountains.—(Botan. zeit., July 6.) G.L.G.

The Physiology of Plants, Volume 2 (1903)
Wilhelm Pfeffer
A diminution of the atmospheric pressure usually causes a distinct acceleration of growth in strongly aerobic plants, and this appears to attain its maximal value when the pressure falls to between a quarter and a seventh of an atmosphere. Growth may then be accelerated to two or three times its original rapidity in some plants (Wieler), while Jaccard observed that potatoes grew seven times more rapidly under such circumstances. The result is due partly to the decreased density of the oxygen, and partly to the decreased air-pressure. Experiments performed by diluting air with indifferent gases show that a reduced partial pressure of oxygen does act as an accelerating stimulus to growth, and the fact that different authors are not in precise agreement as to the respective parts played by these two factors probably shows that the duration of the experiments and the nature of the plant are of considerable importance. Wieler found that a mere diminution of air-pressure produced no effect upon growth, possibly because his experiments lasted for a shorter time than those of Jaccard and Schaible. That duration is a factor of great importance is shown by the fact that prolonged tension may at first produce a retardation, but subsequently an acceleration of growth.
    It is possible that the decreased air-pressure acts by removing a portion of the external pressure antagonizing turgor, and hence increasing the tension exerted by the internal osmotic pressure upon the cell-wall. In any case, however, the action is a stimulatory one, for a correspondingly increased tension of the cell-wall does not produce any mechanical acceleration of growth. This mechanical theory of Schaible's is in fact based upon an erroneous view as to the importance of turgor in growth. Apparently, therefore, either a decrease of air-pressure or a diminution of the partial pressure of oxygen may act as stimuli accelerating growth, although if the time of exposure is short the period of induction may not be sufficiently prolonged for the production of a perceptible result. [Vochting observed (Bot. Ztg., 1892, p. 94) that a reduction of the percentage of oxygen to 3 per cent. suppressed the formation of root-hairs on the roots of the potato.]

Plant-Geography upon a Physiological Basis (1903) p. 69-70.
Franz Wilhelm Schimpe
As Wieler and Jaccard have shown, the pressure within the stratum of the atmosphere in which plants grow does not at all correspond to the absolute optimum pressure for the growth of plants. On the contrary, a diminution of the partial pressure of the oxygen—for the latter only, and not the total atmospheric pressure, comes into question—occasions an acceleration in growth until a certain low pressure is attained, which is constant for each species, and beyond which any further diminution in pressure causes a retardation in the rate of growth. We find this absolute optimum atmospheric pressure for growth to be in the case of Helianthus annuus about l00 mm., but for Vicia Faba about 200 mm. Again, an increase in atmospheric pressure above 760 mm. (or the corresponding pressure of oxygen) up to about 2 1/2 atmospheres occasions a retardation, but after that an acceleration in growth. There are therefore for growth two absolute optima of atmospheric pressure, both of which differ considerably from the pressures that prevail in the inhabited stratum of air, the one being at a far lower, and the other at a far higher oxygen-pressure.
    According to Jaccard a decrease in the pressure of oxygen occasions not only more rapid growth, but also richer branching in the axes and roots, as well as an increase in the size of the leaves.

Floricultural Cabinet, July, 1854: 180
Atmospheric Influence On Plants.—The pressure of the atmosphere has a decided influence on the form and life of plants. From the abundance of their leafy organs provided with porous openings, plants live principally in and through their surfaces; and hence their dependence on the surrounding medium. Animals are dependent rather on internal impulses and stimuli; they originate and maintain their own temperature, and, by means of muscular movement, their own electric currents, and the chemical vital processes which depend on and react upon those currents. A species of skin respiration is an active and important vital function in plants; and this respiration, in so far as it consists in evaporation, inhalation, and exhalation of fluids, is dependent on the pressure of the atmosphere. Therefore it is that alpine plants are more aromatic, and are hairy and covered with numerous pores. For according to zoonomic experience, organs become more abundant and more perfect in proportion to the facility with which the conditions necessary for the exercise of their functions are fulfilled, as I have elsewhere shown. In alpine plants the disturbance of their skin-respiration occasioned by increased atmospheric pressure, makes it very difficult for such plants to flourish in the low grounds. The question whether the mean pressure of the aerial ocean which surrounds our globe has always been the same, is quite undecided; we do not even know accurately whether the mean height of the barometer has continued the same at the same place for a century past. According to Poleni's and Toaldo's observations, the pressure would have seemed to vary. The correctness of their observations has long been doubted, but the recent researches of Carlini render it almost probable that the mean height of the barometer is diminishing in Milan. Perhaps the phenomena is a very local one, and dependent on variations in descending atmospheric currents.—Humboldt's Aspects of Nature.

Root bound; root pruning

Stout: Cyclic Manifestation of Sterility in Brassica pekinensis and B. chinensis. Botanical Gazette 73:110-132 (1922)

Child: Certain Aspects of the Problem of Physiological Correlation Bot. Gaz. 8(6): 286-295 (June, 1921)

Root-bound / Root pruning

Girdling, Ringing, Binding