Experiment Station Record, 12: 947-952 (1901)

The condition of success with grafts
L. DANIEL (Rev. Gén. Bot., 12 (1900), Nos. 141, pp. 355-368; 142, pp. 405-415; 143, pp. 447-455; 144, pp. 511-529).

The author reviews the earlier beliefs respecting conditions necessary for the successful grafting of plants on each other, defines certain terms used in grafting, and gives the conditions necessary for success in grafting a large number of plants belonging to different species, genera, and families.

Grafts are divided into two groups—grafts by approach, or anatomical grafts, and true or physiological grafts. The graft properly called, or physiological graft, is divided into two classes—ordinary grafts and mixed grafts. There is an ordinary graft proper when the stock is deprived entirely of its assimilating apparatus and the scion of its absorbing apparatus. In the mixed graft proper the stock may preserve part or all of its assimilating apparatus, and the scion part or all of its absorbing apparatus. In grafting by approach success is considered to be attained when the two plants grow together in an enduring manner, so that if separated a wound is formed. The graft proper is said to succeed when after having lived a certain length of time on the stock the scion fructifies and produces fertile seeds.

The conditions of success of grafts are divided into two groups, extrinsic conditions, i.e., conditions independent of the nature of the plant, as soil, temperature, etc., and intrinsic conditions, or conditions dependent upon the peculiar nature of the plants grafted, as method of cicatrization, analogy, and botanical relations. The extrinsic conditions which it is necessary to observe in grafting by approach are summarized as follows: (1) A temperature sufficient for the production of the meristem, (2) the prevention of all conditions which cause rotting or drying of the cicatrizing meristem, and (3) maintenance of adherence of the wounds by the aid of ligatures susceptible of being loosened progressively with the growth of the plant.

Under intrinsic conditions in grafting by approach cicatrization is first considered. Plants cicatrize their wounds either by simple drying of the cut tissues and neighboring cells or by regeneration of tissues by the aid of the meristem. The author thinks it may be possible to graft plants by approach which cicatrize the wound by drying up, but this could be accomplished only by compression when operating with very young tissue in a way to produce an artificial concrescence. This last method has not been tried, but all methods by cutting have failed in the divers monocotyledons and the majority of the cryptogams. Thus the author has not been able to graft Ruscus, ferns, bamboos, or maize, and hence formulates the fourth fundamental condition of success in grafting by approach as follows: Grafting by approach is impossible with all plants which cicatrize their wounds by desiccation of the wounded cells and neighboring tissues-that is to say, are incapable of regenerating their tissue.

In order to learn whether only plants possessing cambium tissue are able to be grafted, as generally held, the author operated on a number of monocotyledons and cryptogams. A perfect cicatrization of the wound was obtained by the tongue graft with Gladiolus, Funckia cordata, day lily, Philodendron, caladium, white lily, Globba coccinea, etc., but the most interesting result was the success of the cicatrization of Selaginella arborea. The success of these grafts shows that grafting by approach is possible with certain monocotyledons, and that the presence of the cambium layer is not always necessary to the success of all grafts by approach.

Under analogy in grafting by approach, plants essentially different in wood and bark structure are first considered. Borecole and turnip, the structure of which is very different, were easily grafted, forming a perfect suture between the ligneous layer of the borecole and the medullary parenchyma of the turnip. The difference in the hardness of woods and their histological nature may not be an obstacle to anatomical union. A natural, distinct cicatrization occurred between the grafted oak and the beech and between the fir and linden; the oak and the ash united by their stems, and the oak and the walnut united by their roots. The rose and the grape have also been united. Nevertheless, the graft by approach does not always succeed between plants so different. Thus the author endeavored in vain to graft the horse-chestnut and the common chestnut.

The author considers analogy in cell contents as affecting the graft by approach, and it is shown that the accumulation of reserve material in different vegetative parts of plants has no special importance in grafting, as is proved by the success attained in grafting by approach the turnip and cabbage, borecole and kohl-rabi, Brussels sprouts and kohl-rabi, and kohl-rabi and cauliflower. Even grafting by approach between roots of lettuce and aged salsify succeeds, though the inulin of the salsify roots is not able to circulate in the cell membrane of the lettuce. But if the cell contents of one of the plants approached are toxic for the other, the graft fails. Thus the author was not able to graft celandine and salsify, salsify and burdock, etc.

Under analogy in method of development, it is shown that if a large and a small variety are grafted on each other, the larger variety will develop to the detriment of the smaller, which will remain nearly dwarf. Plants of different forms, like borecole and cauliflower, may make good unions. Plants in active condition of growth may be grafted by approach on plants at rest. Thus a seedling cabbage several weeks old was grafted in the springtime on a turnip, the root of which was already completely formed. The graft succeeded perfectly. The graft by approach succeeds between annuals, biennials, and perennials. Thus peas, sweet peas, and toad flax have been united. The symbiosis ceased at the death of the annual species. The same fact was observed in grafting by approach biennial and perennial plants. The success of the graft between the fir and the linden, and Aralia spinosa and A. sieboldii, shows that deciduous and evergreen plants may be grafted on each other.

With the graft proper, as with the graft by approach, all of the extrinsic conditions, such as temperature, rotting and drying of the meristem, and necessity of contact of the wounds, are present, but in cutting off the top of the stock and suppressing the absorbing apparatus of the scion there is danger of the death of both plants. Another fundamental extrinsic condition of success, then, must be the maintenance of the life of the two plants until success is complete. The scion is sometimes preserved by placing it in water as soon as it has been prepared. This prevents it from drying out, keeps the cut surface clean, and prevents the formation of sugar or other materials on the cut ends which might interfere with the free passage of sap from stock to scion, and is recommended.

In order that the scion may be able to grow, it is necessary to reestablish the turgescence of its tissues. This reestablishment is made by imbibition of the crude sap of the stock by the cells of the scion. The reestablishment of turgescence is effected more quickly according as the crude sap is presented in considerable quantity, but also more quickly if the initial turgescence of the tissues of the scion has not been diminished during the preparation of the graft and its putting in place. This explains why it is necessary to operate quickly and why the cutting of the graft under water, where the scion preserves in a large part its turgescence, produces such good results. It also accounts for the good effects of the wax-like material in grafting in the open air; the utility of the collar graft, because the osmotic force is strongest at this level; and the importance of the time of day in operating, because the osmotic force varies in the course of the day, being strongest in the evening (hence the greater success of grafting in the evening). The reestablishment of the turgescence in the graft is cited as a fundamental condition of success, therefore it is not possible to graft parts of plants which are incapable of retaking their turgescence or which do not possess it entirely.

Under intrinsic conditions, it is shown that in the graft proper, as in the graft by approach, plants incapable of regenerating their tissues can not be grafted. The author succeeded in grafting by the graft proper the white lily, Gladiolus, Funckia cordata, etc., when operating on young stems. In all these grafts the anatomical cicatrization was effected by the parenchymatic tissues. No liber or fibrovascular structure was observed to form between scion and stock. The transport of the sap was thus singularly hindered, and at the end of a variable period one of the parts, or both, died. By utilizing the aerial roots, which some of the monocotyledons possess, to supplement the absorption of the scion, success was attained with a number of plants. This shows that the nonsuccess of the graft with monocotyledons capable of regenerating their tissues comes from insufficient vascular communication, since it becomes possible when a complementary absorption apparatus is supplied.

Plants with active cambium layers, which may be grafted by approach, can not always be grafted by the graft proper, since the common European bean (Faba vulgaris) and the kidney bean, which graft easily by approach, have always failed when grafted by the graft proper, no matter what precautions were taken.

Differences in wood and bark are not obstacles to success in the graft proper. Thus there is a great difference in the thickness and strength of the safflower and the annual sunflower; between the sunflower and the Jerusalem artichoke; the young cabbage and the root of the turnip; the root of the cultivated carrot and that of fennel; nevertheless, these plants united perfectly. These same facts were observed with trees, the graft succeeded between the chestnut and the oak, the pear and the hawthorn, the hawthorn and the quince, in spite of the marked differences in the barks. From these and other grafts, it is concluded that hardness, density, and elasticity of wood play a secondary role in the success and duration of grafts, but it is not the same with conduction. When the differences of sap conductions are too great the grafts will not succeed. As an example may be mentioned the grafts between the lilac and ash, cherry and almond, cotoneaster and chestnut, etc., which grow the first year, then die without fructifying. The duration of the graft is then very variable and depends for its value on the differences in conduction between the scion and the stock. Thus the pear grafted on the quince endures for a shorter period than the pear grafted on the pear seedling. When the differences of conduction are too great between two plants, the mixed graft is sometimes used successfully where the ordinary graft fails. By the use of the mixed graft the author was able to unite Vernonia proealta and Xanthium macrocarpum, which failed by the ordinary process of grafting.

The author has succeeded in grafting plants whose cell contents presented very marked differences. Thus the grafts of Chicoriaceae and of divers Euphorbiaceae, etc., show that plants with different latex contents succeed, although it has been previously held that plants with a milky juice could not be grafted.

A number of grafts were made to determine what influence reserve material in plants might have on grafting. The easy grafts on roots of the carrot and parsnip show that the presence of reserve material is no obstacle to success. The graft of the tomato on the potato, annual sunflower on the Jerusalem artichoke, etc., show that the formation of tubers on the stock takes place even when the scion is incapable of producing tubers itself. In grafting in September a young cabbage on the purple-topped turnip, which would have commenced to form its tuber in October, the turnip tuber formed only the month of April following, when the scion became plethoric. It is then the scion which by its mode of nutrition commands the function of reserve material in the stock.

The inverse graft of plants susceptible of forming tubers on a plant which does not yield tubers may be realized. Thus the author succeeded in grafting Helianthus laetiflorus, species with enlarged rhizome, on H. annuus, an annual species not forming tubers. The scion grown entirely above the soil was unable to form tubers. The reserves which were formed passed into another form in the stock, which took a development altogether abnormal and became very ligneous. The potato grafted on eggplant and tomatoes has been observed to form aerial tubers and thus store up its reserve material.

Analogy in habitat seems to be a more or less important factor. Thus Phlox decussata, which grows in humid soils, has not been successfully grafted by the author with P. subulata, which grows on dry soils; though parsley, which prefers a dry soil, succeeds when grafted with Sison ammomum, which prefers a humid soil. In the case of trees, pears are grafted on quince in rich soil and on pear seedlings in poor soil, etc. Different soils then are not the most serious obstacles to success in grafting, but they seem to have more or less marked influence on the duration of the graft.

If a dormant ligneous scion is grafted on an active ligneous stock, success follows, but does not follow if conditions are reversed. With herbaceous plants, an active scion may be grafted on a dormant stock and succeed. When the scion and stock do not come into activity about the same time, the graft may succeed, but the duration of the graft will be shortened.

In order to study the limits of the possibility of grafting, experiments were made with the following families of plants: Rosaceae, Umbelliferae, Leguminosae, Cruciferae, Solanaceae, and Compositae. With Rosaceae, Leguminosae, and Cruciferae, the limit of grafting seems to be confined to genera of the same tribe. With Solanaceae and Umbelliferae, grafts were successfully made between different tribes. With Compositae the limit of grafting seems to be the subfamily.

Daniel bibliography