Van Mons’ Theory of Fruit-tree Breeding

One thing is certain: Van Mons, the Belgian plant breeder, introduced many improved forms of pears and other fruit trees. How he accomplished this has been debated vigorously. Some writers praised Van Mons' theory, while others attempted to discredit it by appeal to their own prejudices. Some experimenters (e.g., Rivers, 1855) claimed to have failed when they followed Van Mons' methods, even though they chose only one or two aspects of that method.

Part of the confusion surrounds the word "variety", which is even more vague and uncertain than "species". Apparently, Van Mons did not regard his productions as new varieties—"Nature alone creates". DeVries (1909) wrote:

He found all the sorts which he cultivated and put on the market, growing as such in the wild state and, as it happened, almost all of them in the Ardennes. The wild plants were thorny and their fruits small, tough and woody. As the result of being sown in a garden and under the influence of another climate they regularly lose their thorns and the tough consistency of their fruits, which become larger, fleshier and juicier. But the differences in form, color and taste and other valuable characters arose neither in, nor as a result of, cultivation; they already existed in the wild forms. His new kinds are nothing more nor less than already well-known cultivated forms which he has improved in respect of size and juiciness, by selection for two or three generations without altering their varietal characters in the very least. Van Mons was fully aware of the independence and constancy of these forms and it should be noted that he speaks of them as subspecies and not as varieties.

In this sense, size and fleshiness are not to be considered as varietal characters on the same level as form, color and taste. This may strike some readers as odd because we commonly regard a tree or strain that bears large fruit to be varietally distinct from one that bears small fruit; just as we regard a dwarf tree to be a different variety than a tall or columnar or weeping one. But sometimes our assumptions are mistaken. We do not assume that a 'Granny Smith' apple tree grafted to a dwarfing stock is a different variety than one on its own roots. And though a trumpet vine grafted to a catalpa may lose its vining character, we do not call it a new "variety".

Part of Van Mons' method was to collect pears before the seeds had matured, then left the fruit to rot before removing the seeds for planting. Other experimenters have done the same things with different fruit-bearing plants.

Goff (1891) found that, "The results suggest that in our climate, the tomato, at least its more rampant growing varieties, may be rendered more productive and earlier in maturing by a treatment that reduces the native vigor of the plant." Furthermore, "The firmness of the fruit from the immature seed has been somewhat less than that from the ripe seed, the rind being slightly thinner." This is just what Van Mons accomplished with pears. Similarly, Brown (1874) wrote, "...we are told by Von Martius that the Brazilians always propagate Willughbeia speciosa by unripe seeds, considering that the fruit from plants thus obtained is better than that from trees grown from matured seed." Hemsley (1878) reported similarly, "it is stated that the Brazilians always employ unripe seeds to propagate Hancornia speciosa, a valuable fruit tree, believing that the fruit borne by trees raised from immature seeds is of a superior quality." [Apparently Hemsley and Brown were referring to the same species, Hancornia speciosa Gomes. The allied genus Willughbeia is native to Borneo and Malaysia.]

Michurin (1915) observed the same superiority in pears raised from unripe seed:

In the autumn of 1901 about a dozen seeds—not fully ripe and still rather whitish, it should be noted—were taken from three hybrid fruits of a Ussurian pear tree that had been fertilized by pollen taken from a basket specimen of a Beurré Diel pear tree, and were planted in a box in the open air. The other four fruits were kept until January and the seeds taken from them were planted in the same box only in spring. After sprouting, the seedlings were lined out in beds. No sharp difference was noted either as regards the loss of shoots or the development of seedlings from the two plantings, but later when the trees bore fruit the difference did not fail to manifest itself in a somewhat original manner, namely, the trees of the second, spring, planting in which the dried seeds had been used, started fruit hearing in 1910, and also in 1911 and 1912, whereas the trees of the first, i.e., autumn, planting in which fresh, undried seeds had been used began fruit bearing only in 1913, but the quality of the fruits of the trees that grew from the dry seeds was incomparably worse. In the first place, they all proved to be early-summer ripening fruits, unfit to store for winter, and as regards taste they were very viscous, a characteristic of the Ussurian pear, although in size they were four limes as large as the fruits of the maternal tree. Then altogether inexplicable was the fact that all these trees of the second, spring, planting were less hardy to our climate and especially to the scorching of the stem's bark by the sun. In contrast, three trees of the first, autumn, planting, when fresh seeds were used, yielded, firstly, late-ripening fruit capable of keeping in winter storage until the end of December, a great advantage for new varieties in orchards of our localities in Central Russia, and, secondly, the fruits have an excellent flavour and a flesh that is without granulation and melts in one's mouth. Moreover, the trees themselves are noteworthy for complete hardiness to the climate of our locality, and of all our pear-tree varieties they are the only ones the bark of which does not suffer from sun-scorch.

As for allowing the fruit to rot, Desai (2004) wrote, "Upon extraction, the seeds were subjected or not subjected to fermentation, washing, and drying. Cucumber, melon, and watermelon reached full germinability by 35 dpa [days past anthesis], but squash required a longer period. Fermentation and drying were important for improving the germinability of immature seeds of cucumber, melon, and watermelon. Fermentation had a deleterious effect on immature seeds [of squash], but drying and washing improved germinability of squash seeds."

Similarly, Peter Gideon, the "father" of Minnesota apples, explained in 1899, "I have had very good success with planting the cores, or the pomace fresh from the cider press, covering not more than one inch deep." Again, the seeds were in contact with the rotting or fermenting pulp.

It is not surprising that germination of some seeds would be improved by this fermentation. Such seeds are commonly swallowed by fruit-eating animals, and must survive passage through their digestive systems. As Waldron (1891) reported:

The roses that grow the most abundant and fruitful [in North Dakota] are the Rosa blanda and the Rosa Engelmanni. The latter has a large fruit about two and one-half times long as broad, is rather juicy and of a flavor much like the thorn apple [Crataegus coccinea]. The rose hips of both species are eaten readily by the prairie chicken, grouse, antelope and rabbit, the indian also comes in for his share. I have seen this fruit in such quantities over large areas that it would have furnished food for hundreds of sheep.

Van Mons also insisted that seeds from young trees, bearing their first fruits, gave seedlings that varied in the preferred direction—assuming a more domesticated form—than seeds of old trees. Poiteau (1836) explained:

As soon as the young pear tree with which began his experiments, produced its first fruit, Mr. Van Mons sowed the seeds. There resulted a first generation, the individuals of which,  although of very different kinds, did not resemble their parent. He cultivated them with care, and endeavored to hasten their growth, as much as possible, by all the known means in his power. These young trees yielded fruit, which were generally small, and almost all of them bad. He sowed the seed of these and obtained a second generation without interruption—which is very important—that were very different in kind, but did not resemble their parent, although they had a less wild appearance than their predecessors. These were cultivated with equal attention, and they fructified earlier than had the parent. The fruits of this second generation, also varied as much as the trees which bore them, but part of them appeared less near the wild state than the preceding; yet only a few possessed the requisite qualities to entitle them to preservation. Constant in his plan, Mr. Van Mons sowed the seeds and obtained a third continued generation, the greater part of the young trees of which, had a phasis of good augury, that is something of the physiognomy of our good domesticated pear trees, and they were consequently less various in appearance. Being carefully cultivated, as had been the preceding, these trees of the third generation, fructified earlier than the second generation. Several of them produced edible fruit, although not yet decidedly good, but sufficiently ameliorated to convince Mr. Van Mons that he had discovered the true path of amelioration, and that he should continue to follow it. He also recognized, with no less satisfaction, that the oftener the generations succeeded each other, without interruption, from parent to son, the more promptly did they fructify. The seed of the fruits of this generation, which had a good appearance, were sowed, and the trees managed as carefully as the preceding, and produced a fourth generation, the trees of which were a little less varied, and nearly all of them had an appearance of favorable augury; they fructified in a shorter time than the third generation; many of the fruits were good, several excellent, but a small number still bad. Mr. Van Mons took the seeds of the best kinds of these pears, sowed them and obtained a fifth generation, the trees of which were less various than the preceding, fructified sooner, and produced more good and excellent fruits, than those of the fourth.

Can the seeds of young trees yield plants of a different character than seeds of the same trees when older? Olsson-Seffer (1907), discussing rubber trees, reported:

    I have noticed that seeds from young plants are fuller and more rounded than those from older trees. The seedling from such a seed has smoother and bigger leaves than those developing from seeds with a loose seed coats and ribs on their surface.
    The root development is much stronger in a seedling from seed taken from a younger tree, and this is another reason why careful attention should be paid to the age of the parent tree.

Most of the changes noted above cannot be considered as "varietal" because they are conditioned by specific treatments that must be repeated each generation.

What exactly were the seedling characters that Poiteau described as having a "phasis of good augury"? Neill (1823) explained that, "Whenever a seedling indicated, by the blunt shape, thickness and woolliness of its leaves, or by the softness of its bark and fulness of its buds, the promise of future good qualities as a fruit-bearing tree, a graft was taken from it, and placed on a well-established stock: the value of its fruit was thus much sooner ascertained."

Visser (1965) found a strong correlation between the absence of juvenile characters in apple seedlings and precocity. That is, seedlings that showed more juvenile (or "wild") characters generally came into bearing later than those with fewer such characters. And Visser & De Vries (1970) further found a correlations between precocity and productivity in apples and pears. De Vries (1976a, b) found similar correlations in roses. De Vries & Dubois (1977) also found a correlation between length of juvenile period and the length of flower stems in roses.

It was Van Mons' belief, in taking wildlings into cultivation for amelioration, "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." (Downing, 1849)

Hansen (1904) also found increased variation in sccdlings of the Western Sand Cherry (Prunus besseyi). "The third generation is decidedly more variable than the first."

Root-pruning would seem necessary to counter the increased root development noted above by Olsson-Seffer. However, root pruning is also an old technique for hastening fruiting in trees.

It is to be expected that when raising seedlings from a single parent, and then raising seedlings from them, some degree of inbreeding decline would result—even though there was probably some crossing among the siblings. Van Mons' technique of planting the saplings closely in the nursery rows would have allowed him to identify those specimens which retained more of their constitutional vigor. That is, specimens that managed to flower and fruit despite crowding would undoubtedly be more productive, when given more room, than siblings that failed to flower. Troyer (1976) similarly observed an increased tendency towards production of multiple ears while selecting for earliness in corn. "We observed a cycle-by-density interaction wherein advanced cycles exhibited prolificacy at a low density after selection against barrenness at high densities."

It is apparent from Poiteau's account that part of Van Mons' success was in the selection and selective improvement of certain charcters. This is what is commonly understood as "selective breeding". However, the rest — particularly the use of immature seeds from young trees — is more properly described as "Physiological Predetermination".

Vibert (1846) seems to have been following a breeding plan similar to that of Van Mons:

“I was at Rouen in September 1829, at the home of an English plantsman [W. C. Calvert] whose garden had been left to itself for a while, and noticed there, among the seedlings, a semi-double rose blooming, which, aside from its remontant qualities, showed characteristics I hadn’t seen in other sorts. Some cuttings of this rose were given to me, and, as the place had the name ‘Trianon,’ that is what I named the rose. Having sown seed of this rose for 8 or 9 years without having gotten more than one good variety, I sowed instead the seed of some flesh-colored semi-doubles [presumably offspring of the original Trianon] with foliage that was different; after having repeated this for three or four years, I was able to raise a white; and the seeds of this were what I subsequently sowed, for the most part. The greater part of my seed-bearers are in their 5th or 6th generation; and it is really quite extraordinary to see such diversity among plants springing from the same Type . . . The number of roses descending from my Perpetual Trianon, doubles and semi-doubles, has surpassed 40, and I am sure to add many to the number of doubles before too many years have passed. Many of these roses bloom in clusters of 50 to 60 blossoms; their diameter varies from 3-8 cm [ca. 1-3 inches]; most waft an elegant perfume. From purest white to light purple, all shades are found; but, above all, it is in the details of their appearance that Nature has exercised freedom: wood, leaves, thorns, manner of growth—all vary . . . Such, then, are the reasons I have set up a new division of Perpetuals . . . Let me add an important observation: Within this set of roses are plants which bloom the first year from seeds, which does not ordinarily happen with Chinas, Noisettes, or Bourbons; last year, 10 or 12 young plants bloomed in July. All of these roses coming from this Trianon seem to me to be very receptive to pollination from other varieties—or perhaps it is because of their own inherent qualities that they show so much variation, which seems to me to be the more likely explanation [signed: Vibert, Angers, June 28, 1846].”

Vibert's rose seedlings apparently varied more than Van Mons' pears because they originated with a hybrid—the "Trianon" rose, perhaps similar to Portlandica, and possibly pollinated by a Noisette. I do find it odd that Vibert's Chinas and Noisettes were so slow in blooming. Perhaps I am surprised only because other breeders of the time followed the same program, increasing the precocity of garden roses in general. According to a writer in The Florist and Pomologist (1882):

"Adverting to the influence of selection on precocity, M. Carrière mentions the fact that while the seedling Roses of fifty years ago took six or eight years to produce their flowers, it is not now unusual to see them flowering the first year. There is, however, great variation in this respect between seedlings derived even from the same fruit, some seedlings requiring four, and others from eight to twenty years to fruit. The Duchesse d'Angouléme Pear only began to produce fruit thirty years after it was raised from the seed."

Van Mons insisted that seedlings raised from the first fruits were more variable than those raised from seeds of mature plants. This may relate to phenotypic plasticity, where a given trait is more easily influenced by environmental conditions, and more subject to vegetative selection for extreme expressions. Breese, et al. (1965) found that Lolium perenne clones that had been propagated vegetatively for many years did not respond to somatic selection for greater or lesser production of tillers. To the contrary, seedlings responded more significantly.

* A cockade is a knot of ribbons, usually worn on a hat, to indicate
political allegiance. The Austrian cockade is black and yellow.

Another aspect of Van Mons' system seems to have been Genetic Transilience. This is particularly noteworthy in his discussion of a line of roses he had grown. In some selections, the flowers increased in fullness in subsequent generations, but the form and color did not vary in a useful way. In other selections, color and form were the predominant improvements. "We obtained several duplicates of the plants which had been late in bloom, and amongst other things the cocarde d'Autrich [Austrian cockade*], which was quite black, and which was taken from me when it came to flower."

(to be continued)