Proc Natl Acad Sci U S A. 5(2): 36-37 (Feb 1919)
THE CAUSE OF PROLIFERATION IN BEGONIA PHYLLOMANIACA
ERWIN F. SMITH
LABORATORY OF PLANT PATHOLOGY, UNITED STATES DEPARTMENT OF AGRICULTURE
Read before the Academy, November 18, 1918

Bailey: Cyclopedia of American Horticulture, A-D (1900)

The cause of the excessive production of adventive shoots on the leaves and internodes of this plant (a very strange phenomenon) is attributed to excessive loss of water, due to woundings or other causes. Usually in regeneration the response is not far from the place of injury, here it may be at a long distance from the wounded part, e.g., roots wounded and response in the top of the plant, although a direct response from the injured part can also be obtained. The paper will be published in full in The Journal of Agricultural Research. The following is a synopsis:

1. Ordinary begonia leaves when detached from the plant and pegged down on moist sand develop roots and shoots from cut places and this method is used by gardeners for the propagation of begonias. Many other plants are propagated in this way, e.g., the hyacinth from bulb scales.

2. But the leaves and shoots of this begonia proliferate while still attached to the plant.

3. They will proliferate on the plant very freely when wounded, making small forests of shoots on the thickened red lips of the wound if the wounds are made in quite young tissues, but not otherwise (young leaf blades were used).

4. They will frequently proliferate in the top parts of cuttings (on leaves and internodes) especially if the cuttings are dried for a day or two before planting.

5. They will proliferate most astonishingly at the top of the plant (both from leaves and internodes) if the roots are wounded, but here again only quited young tissues can be shocked into the production of such shoots. This is the most striking fact I have discovered, viz., that the prolification may occur at a long distance from the place of wounding and must be from young tissues. So far as known to the writer, it is the first example of response of this sort at a distance from the point of injury.

6. I have also some evidence that leaves will proliferate locally under colonies of sucking insects (mealy bug, white fly), also that withholding water from the plant for a few days will cause it to proliferate.

7. The nature of the shock appears to lie in the sudden interruption of the water current which is conceived to cause cell-precipitates or plasmolysis of young totipotent cells which begin to grow when they have recovered from the shock.

8. The prolification at times is so much like a forest that one must assume that the whole surface (epidermis) of immature shoots is full of cells capable of growing into new plants if properly shocked but that as the tissue matures these cells either lose their power of response, or become more perfectly protected.

9. These adventive shoots, for the most part, perish quickly and cannot be regarded as branches, since they have no initial connection with the ordinary cambium, or xylem-phloem of the mother plant. They are rather to be classed with filial teratomas. Later, a small proportion of them establish connections with the conductive tissues of the mother and persist, i.e., become abnormally situated branches.

10. My observations contradict those of Prillieux and confirm those of Verlot and of Caruel that buds may arise from the ordinary trichomes. They may develop either from the base or the middle of acicular hairs. Such hairs arise from a red tissue, the other parts of the epidermis being green. I have also seen them developing from the base of glandular hairs which are abundant on the young internodes, but they are not restricted to these pairs.

Botanical Magazine 87: t. 5254 (1861)

Problems of Genetics pp. 50-53 (1913)
William Bateson

It is interesting to note that sometimes as an abnormality, the faculty of division gets out of hand and runs a course apparently uncontrolled. A remarkable instance of this condition is seen in Begonia "phyllomaniaca," which breaks out into buds at any point on the stem, petioles, or leaves, each bud having, like other buds, the power of becoming a new plant if removed. We would give much to know the genetic properties of B. phyllomaniaca, and in conjunction with Mr. W. O. Backhouse I have for some time been experimenting with this plant. It proved totally sterile. Its own anthers produce no pollen, and all attempts to fertilise it with other species failed though the pollen of a great number of forms was tried.

17 Bull. Soc. Bot. de France, xxxiv, 1887, p. 182.

Recently however we have succeeded in making plants which are in every respect Begonia phyllomaniaca, so far as the characters of stems and leaves are concerned. These plants, of which we have sixteen, were made by fertilising B. heracleifolia with B. polyantha. They are all beginning to break out in "phyllomania." As yet they have not flowered, but as they agree in all details with phyllomaniaca there can be little doubt that the original plant bearing that name was a hybrid similarly produced. The production of "phyllomania" on a hybrid Begonia has also been previously recorded by Duchartre.17 In this case the cross was made between B. incarnata and lucida. The synonymy of the last species is unfortunately obscure, and I have not succeeded in repeating the experiment.


Fig. 5. Piece of petiole of Begonia phyllomaniaca. The proximal end is to the right of the figure.

From these facts it seems practically certain that the condition is one which is due to the meeting of complementary factors. At first sight we may incline to think that the phyllomania is in some way due to the sterility. This however cannot be seriously maintained; for not only is sterility in plants not usually associated with such manifestations, but we know a Begonia called "Wilhelma" which is exactly phyllomaniaca and equally sterile, though it has no trace of phyllomania. This plant arose in the nurseries of MM. P. Bruant of Poitiers, and has generally been described as a seedling of phyllomaniaca, but from the total sterility of that form this account of its origin must be set aside.

The phenomenon in this case can hardly be regarded as due to the excitation of dormant buds, for it is apparent on examination that the new growths are not placed in any fixed geometrical relation to the original plant. They arise on the petiole, for example, as small green outgrowths each of which gradually becomes a tiny leaf. The attitude of these leaves is quite indeterminate, and they may point in any direction, some having their apices turned peripherally, some centrally, and others in various oblique or transverse positions (Fig. 5). These little leaves are thus comparable with seedlings, in that their polarity is not related to, or consequent upon that of the parent plant. They have in fact that "individuality," which we associate with germinal reproduction.