Manual of Plant Diseases (1922)
Prof. Dr. Paul Sorauer

DWARF-GROWTH (NANISM)

The dwarf conifers found in trade under the name "Japanese or Chinese Trees of Life" show an interesting effect of the influence of a limited soil space. The figure on the next page illustrates a living specimen which has been classified by the well-known firm J. C. Schmidt (Berlin) as Thuja obtusa and kindly placed at our disposal. The tree, with the pot, is 86 cm. high in all,—and 60 cm. high above the soil. At its greatest width the crown is 80 cm. across. The base of the trunk, divided into several protruding ridges, has a diameter of 19 cm., the trunk at the height of the crown, where the branches appear, one of 12 cm. This healthy specimen, with a dense crown, whose age is estimated to be 100 years, cost $87.50.

1In an article on "dwarf growth in the vegetable kingdom,"* Grube quotes a report by Sir Geo. Staunton, from "des Grafen McCartney Gesandtschaftareise nach China," Berlin 1798. Staunton saw in Ting-hai, spruces, oaks and orange trees none of which were more than 2 feet high and on which fruit had set abundantly. At the base of the trunk the soil was covered with layers of stones weathered and covered with moss giving the pots the appearance of great age. "Throughout China, there is a great liking for these artificial plant dwarfs for we found them, as a rule, in every house of any pretention whatever." It is there further related that the "liliputian" trees were propagated by binding loam or garden soil around different branches. This was kept moist until the branches developed new roots in the earth ball; they were then cut off. We still use this process in the layering of branches or top shoots and the covering of the cut places with moss. This plan was followed in China, because it had been observed that an artificially produced dwarf character is hereditary. When the tendency has become hereditary It is strengthened in the new individual by turning down the end bud of the main shoot and bending it with wire in another direction. "If it is desired to give the dwarf tree the appearance of an old, already half dead tree, the trunk is often covered with syrup to attract ants and these, after they have eaten the sweet, immediately injure the bark, giving it thereby a brownish, half-weathered appearance."
     Rein** describes the Japanese process which is somewhat different. They call the dwarfing or "Nanisation" "Tsukurimono." This expression is not used in the new book by Ideta.***. According to Rein, the dwarf growth is secured by choosing especially small seeds from under-developed plants. These little trees are pruned and transplanted frequently into as small pots as possible. The cross-section described above in the text shows this. Further, the trunk and branches are twisted and bent toward the horizontal. It Is said that the root ball is cooled. Among varieties of plants used especially in Japan for the growth of dwarfs are mentioned the toy varieties of Acer palmatum, which are budded, "greffe par approache." Further Pinus massoniana and P. densiflora, Podocarpus Nageia, Sciadopytis verticillata. Among fruit trees the Kaki plum. Diospyros Kaki, is suitable for this, the Mume-plum, Prunus Mume and Sakura, Prunus Pseudocerasus, as well as Amygdalus Persica. Among decorative plants are mentioned Evonymous Japonica and the bamboo.

*"Zwergbildung im Pflanzenreich" Gartenwelt, 1904, No. 49.
**Rein, J. J., Japan nach Reisen und Studien. Leipzig, Engelmann. Vol. IT., p. 315.
***Ideta Arata, Lehrbuch der Pflanzenkrankheiten in Japan. 3rd Ed. Tokio, Shôkwahô, 1903.

In literature, notes may often be found referring to the skill of the Japanese and Chinese in growing dwarf specimens of trees, hundreds of years old for table-decoration1.

Our examination of the trunk from a dead tree destroys the halo of the miraculous, with which these productions of Japanese and Chinese horticulture have been surrounded. A section 8 cm. long and 6 cm. at its widest diameter showed most excentric annual rings. The distance of the pith from the bark amounted to 1.5 cm. at one side of the trunk and to 6 cm. at the other. Counting with a magnifying glass showed 30 annual rings on the wider, but only 15 on the narrower side. On the side favored in growth, a great variation in the breadth of the annual rings was noticeable. Four zones could be distinguished. Each of these ended with very slender rings, the tracheids of which had especially narrow lumina and had become browned through resinosis. Otherwise the wood was healthy. In its dimensions the bark corresponds to the section,—i.e., on the side of the narrower rings, it was 1.5 mm. thick, on the other side 4 mm. On the narrower side, a depression was found, in which a scantier development of the wood had been equalized by a thicker formation of bark,—up to 5 mm. There was shown here a tendency to loosen the individual bark scales between the flat cork layers resembling full cork.

Thus the statements as to the great age of the trees are seen to be erroneous These cannot be more than some thirty years old and their dwarf growth, in our opinion, can be obtained by keeping the plants in the very smallest pots until they are root-bound; then transplanting into a large pot, in which the root crown is raised up above the pot in order that the root ball may have full benefit from the soil. After the year of transplantation, wide annual rings are produced at first, which become narrower as the plant becomes root-bound until the growth has become very slight and the last annual ring formed is made up of a few, browned autumn-wood tracheids. In this way the stilt-like trunk bases, borne on the freely exposed root branches, are produced. The crown is probably kept thick by a light cutting back of the tips of the branches, obtaining thereby a greater ramification. In the same way the root balls might have been pruned at each transplanting. We conclude from the porous places filled with full-cork, which occur scattered in the bark, that the trees have been kept wet. At any rate we would have no difficulty in growing trees in such decorative dwarf forms from the genera Thuja, Thujopsis, Biota, Cupressus and similar ones by limiting the soil content.

A corresponding treatment is recommended here and there for deciduous trees and plants. In forcing woody blossoming plants it is desirable to have for sale small specimens as full of bloom as possible. To attain this end, the bushes are planted in small pots, cut back and kept until spring, as long as possible, in cool dark cellars in order to retard the growth beyond the natural time of awakening. Ice cellars serve best in this connection. When vegetation has advanced considerably out of doors the plants are brought out. They now find a very different combination of vegetative factors for the maturing of their growth. Instead of moist spring air, a comparatively slight warmth of the sun and long, cool nights, the plant finds dry, bright, long days with little precipitation. As a result the branches remain short and the eyes easily develop blossom buds.

It will not be out of place to call attention to the fact, that in keeping the bushes in warm cellars, an opposite result is obtained,—namely, absolute unfitness for forcing. The warm, dark place where they are kept produces deformed, very premature shoots, which, when brought at last into the open air, either dry up or gradually and slowly lengthen to whip-like, blossomless wands. The stored-up material has been wasted in the cellar in forming the deformed shoots.

1Sorauer, Einfluss der Wasserzufuhr auf die Ausbildung der Gerstenpflanze. Bot. Zeitung 1873. p. 145.

The most frequent occurrence is dwarfing due to scarcity of water. Like every other organism, the plant has the ability of adjusting itself within wide limits to different conditions. An individual, accustomed from its youth up, to a very scanty amount of water, can pull through with half the amount of water used by a plant of the same species and variety, which had developed with excessive water. Naturally the structure of the whole individual is adapted to these conditions. More thorough investigations have been made with barley1, which was cultivated with a varied water content in the soil (10, 40, and 60 per cent. of the soil's capacity for absorbing water). The most favorable water content for growth might be found possibly between 50 and 60 per cent. of saturation.

2H. Möller, Beiträge zur Kenntnis der Verzwergung (Nanismus), Landwirtsehaftliche Jahrbucher von Thiel. 1883, p. 167.

In the experiment it was shown that the plant even with only 10 per cent, of water had regulated its organization. Little leaf and root substance had absolutely been formed, but the proportion between grain and straw was normal; therefore about as much dry substance in the form of grain as in the form of straw. With the same amount of food in the soil, the dry substance increased as the roots obtained additional water. With too much water, i. e., more than 60 per cent. saturation, very little dry substance was produced absolutely and this small amount was worthless since the proportion between straw and grain was changed,—to the detriment of the latter. Measurement of the leaves showed that the grains grew longer and wider, when water was supplied regularly and more abundantly. These larger leaves, found with a greater water supply, are due partly to the increased number of cells, partly to their greater distention. If the individual cells of the upper epidermis are larger, it may be assumed from the very beginning, that the respiratory apparatus (the stomatal cells) will share in the greater stretching of the upper epidermal cells and will also appear to be the more widely separated thereby. Direct measurement confirmed this assumption, so that therefore for each square centimetre of a leaf grown with abundant water, fewer but larger stomata will be found, than when plants are grown with a scarcity of soil water. H. Möller has determined by experiments2 that plants dwarfed by. lack of water (Nanism) are structurally different from plants whose dwarfishness is due to a scarcity of mineral substances in too weak solutions. In the latter the narrower leaves are probably not due to narrower cells, resulting from water scarcity, but to a smaller number of cells, since measurements show the same cell breadth and the same size of the stomata in plants from a satisfactory nutrient solution and from an insufficiently concentrated one. These differences are easily explained. When the mineral substances are insufficient the cell increase will suffer only from water scarcity. The cells are less distended. As shown by some of Möller's experiments with Bromus mollis, this nanism is not hereditary, since specimens of huge size can be grown from the seed of dwarf plants. Yet, with equal vegetative conditions, seed from normal plants produces more vigorous specimens than that from dwarfed plants.

The case of nanism due to scarcity of nutritive substances, which Möller studied, is not rare in sandy soils. The lack of nitrogen plays the chief part here. This nanism is usually characterized by the fact that, besides the general reduction, the relations of the separately produced organs have been changed. In proportion to the whole growth, the root undergoes a greater distention; but the sex organs suffer a greater retrogression. The number of blossom eyes is very small. Instead of a cluster or a head, there is often only a single blossom. Where a greater number of blossoms are formed single seeds develop which can germinate. It is easy to understand that the leaf-forms are simplified.

In discussing dwarf growth, the phenomena of bud variation must be considered. These have no connection with soil conditions or other external vegetative factors. The form of growth up to this time is so changed by some impulse or stimulus, acting temporarily or persistently, that the organic substance is used up iii the form of more numerous, shorter, usually thicker, short-leaved branches instead of fewer slender, large-leaved ones, in this way producing witches-brooms. In many cases the incitement to such a changed direction of growth may be found in parasitic attacks. The fungus genus Taphrina (Exoascus) especially irritates the branches of various deciduous trees resulting in the formation of witches-brooms (see Volume II, page 179). In other cases we find rust fungi or mites of the genus Phytoptus. Besides these forms due to parasites, however, some surely exist in which other organisms are not active. We find especially in herbaceous, quickly growing plants (Campanula, Pelargonium) the occurrence of a bud disease (Polycladia) as a correlation-phenomenon.

In sickness or loss of blossoming branches, small fleshy bunches are formed, at times, at the base of the stem, made up of closely set bud-eyes, some of which grow out into sickly branches. In diseased thickets growth is often exhausted by a continued new formation of short branches, because the blossoming axes no longer lengthen, but stop growing and turn yellow. In Calluna vulgaris, instead of long blossoming branches, we find blossomless bunches of twigs, pyramidal in form, which might also be called witches-brooms.

In other cases polycladia and bushy forms are produced by the development of normally formed but still dormant lateral eyes, when the buds of the tips have been injured. This takes place when wild growths choke out cultivated ones. In conifers, the heart buds grow out and form bushy crowns, which are called "rosette-growths." The so-called "cow-bushes"—due to injury to beeches, alders, etc., from the grazing of cattle, are similarly explained.

1Tubeuf and Schröter, Naturwissensch. Zeitschr. F. Land- u Forstwirtschaft. 1905, p. 254.

Pure bud variations are numerous. In them the growth in length of the individual branches is restricted without any recognizable cause, resulting in a greater and more rapid development of lateral branches. Among the actual forms of witches-broom, the tendency at present is to place under this head of bud variation the numerous spherical bushes of the spruce witches-broom1. The greatest number of examples is furnished by the many cultivated plants of our gardens in the so-called globe forms of conifers and in the dwarf forms of blossoming bushes. In the short-lived summer plants (Ageratum, Zinnia, Tagetes, etc.) we find that the dwarf growth can become an hereditary peculiarity, persistent in the seed.