Gardiners' Chronicle, ser. 3, 38 (979): 248 (September 30, 1905)

Grafting and Its Results

THE various grafting experiments made by M. DANIEL and others, to which we have from time to time alluded, may seem at first sight as interesting only to the physiologists; but to take this view is to limit our range very unnecessarily, and to deprive ourselves of future practical benefit. It may seem to some mere ingenious trifling to graft an Ipomoea on to a Batatas, or the perennial Sunflower on to the annual species, but when the significance of these experiments is grasped, their potential practical value becomes apparent. The Ipomoea purpurea and the Ipomoea Quamoclit are annuals. Their life-cycle is completed with one complete season. The chlorophyll and other nutritive substances which they are enabled to produce are sufficient for the needs of the plant during its short existence. The Batatas edulis, the Sweet Potato, however, though a plant of the same order, is, in our climate, a slow-growing perennial, and its tubers do not attain their full size till after several years of cultivation. In other words, its reserve store of chlorophyll, and specially of starch, instead of being formed in one season, is accumulated slowly during several years, the light and heat of one season not being adequate for the purpose.

M. DANIEL'S experiments, as mentioned in the Comptes Rendus for July 17, 1905, p. 214, are very interesting from this point of view. The Professor first of all ascertained that ordinary ungrafted cuttings of the Batatas (Sweet Potato) produced no tubers at all in the first season of their growth. But when grafts either of the Ipomoea or of the Quamoclit were placed on the shoots of the Batatas, the tubers were formed immediately on the Batatas stock. In the case of the Ipomoea Quamoclit, which is a less robust plant than the Ipomoea purpurea, the tubers produced as a result of grafting on the Batatas were smaller and less perfectly formed than were those produced under the agency of the stronger-growing scion. In this way the direct relation between the assimilating power of the leaves and the production of tubers, in other words, the amount of accumulation of starch, &c., is plainly evidenced. The greater value of a hardy scion whose foliage does its work quickly as compared with a more tender and less efficient foliage is also manifest. So that if a particular plant be tender and slow growing, its hardiness and its rapidity of development may be enhanced by engrafting upon it a scion of more vigorous habit.

Adverting now to the Helianthus, it will be remembered that H. multiflorus is a perennial with tuber-like root-stocks. In this country it rarely perfects its seeds. The ordinary Sunflower, H. annuus, is, as its name denotes, an annual. Its roots are fibrous, and in ordinary summers it yields abundance of ripe seed. When H. multiflorus is grafted on H. annuus, the grafted plants become stouter and more woody than the ungrafted Sunflowers do, and their roots are very freely produced. The graft remains dwarf, and branches from the base instead of at the top, as does the ordinary Sunflower. It forms also short root-stocks, which die in the winter. Its leaves are more developed, with a thicker cellular tissue, and the crystals of oxalate of lime which are contained in the cells are differently distributed. The flowers are very numerous and produce abundance of well-formed seeds, which, however, owing to the lateness of the blooming period, do not come to maturity. One perfect seed was, however, obtained from the grafted plant, and this when sown produced a plant of Helianthus multiflorus, showing the modications derived from the sunflower stock just alluded to. It was in fact a dwarf sunflower with much developed foliage, but branched at the base.

Observations will be continued for the purpose of noting whether the production of seed, obtained from a scion of an infertile plant grafted on to a fertile stock, will be continued in succeeding generations. It is in any case apparent that we may have it in our power, by the mediation of grafting, to obtain seed on plants which do not usually ripen their seeds, and to establish a kind of compensatory action between seed production and tuber formation.

Experiment Station Record 17: 563

Two examples of grafts, L. Daniel (Compt. Rend. Acad. Sci. [Paris], 141 (1905), No. 3, pp. 214, 215).—Tall morning glory (Ipomoea purpurea) and Quamoclit coccinea were grafted by the author on the sweet potato (Batatas edulis).

The first 2 are annuals, while the sweet potato in that climate is perennial, developing very slowly and producing tubers only at the end of several years. On the other hand, the 2 plants mentioned first are well adapted to the climate. As a result of these grafts tubers the size of 1 cm. were formed at the end of the first year, the tubers formed when Q. coccinea was used as a scion being smaller than when tall morning glory was used. The control sweet potatoes which had not been grafted produced no tubers.

In another instance Helianthus multiflorus, which is perennial and in that climate reproduces itself exclusively by tubers, was grafted on H. annum, a variety of sunflower which grows well there, producing fertile seeds in abundance. As a result of this graft the H. multiflorus scion produced a large number of flowers, one of which contained a fertile seed. From this seed was grown an H. multiflorus which had conserved the characters acquired by the scion.

CybeRose note: According to the folks at the Sand Hill Preservation Center, the production of storage roots in the sweet potato is apparently dependent on heat units; the early varieties requiring less total heat than the intermediate and late types. Therefore, it is probably not a matter of annual vs. perennial, but of heat requirement that allows sweet potatoes to produce storage roots when top grafted by a morning glory or quamoclit. It might be just as useful to graft early sweet potato shoots onto the late types.

Daniel bibliography