Results of Half a Century of Work in Producing
New Varieties of Fruit and Small-Fruit Plants (1929)

Layering Tubes
Ivan Michurin

Fig. 44. New apparatus—tube for rooting cuttings

1The younger the hybrid seedling, the easier it is to root; and on the contrary, cuttings from old trees take on with much more difficulty.
2The diameter is about 2 mm. less than the outside diameter of the given cutting near the place where the ring of bark is removed.

My methods of rooting plant cuttings and planting them in the middle of the summer with fully-developed leaves, methods which I have employed with particular success in propagating and at the same time improving the qualities of new hybrid varieties of pears, are as follows. In the latter half of the spring, on the cutting A (see Fig. 44) from a one- or two-year-old 1 shoot 20 cm. in length, which may be branched, a strip of bark B 5 to 8 mm. wide is removed, and forthwith a rubber tube, C, prepared beforehand, is put over the bared part; the tube is 60 mm. long, outside diameter 12 mm., thickness of the walls 2 mm.; consequently, the internal diameter will be 10 mm. In the middle of this piece of tube two apertures2 are bored through both walls with the aid of a sharp-pointed steel tube worked with a revolving motion; then, half the tube is slit from the tip to each of the apertures in the walls.

The tube prepared in this way is slipped on to the part of the cutting that has been bared of bark B. It closely grips the bark of the cutting on the lines above and below the bared ring. Both halves of the remaining parts of the incised rings are inserted in one of the ends of a glass tube D bent at right angles and having an internal diameter of 12 mm. If a bent glass tube is not available a straight piece F 10 cm. long, of the same diameter (see Fig. 45) may be used.

Fig. 45. Straight tube (F) for rooting cuttings

Moreover, in order that the rubber shall grip the bark of the shoot more tightly, the tube is tied in criss-cross fashion with thick cotton thread and smeared with liquid grafting wax; the other, slit end of the rubber tube is stopped up with a cork (see Fig. 46). Then, into the open end of the glass tube, which is fixed in a vertical position, boiled water is poured; as the water in the tube evaporates, it must be replenished; and to prevent putrefaction the water must be changed every week, using cooled boiled water.

If this regime is adhered to for a period of five to seven weeks, according to the species and variety of plant, a callus will first appear in the gap of the rubber tube and then roots, and the shoot above the tube will thicken considerably thanks to the deposits of nutritive substances furnished by the leaf system and retarded in its downward movement by the removal of the strip of bark. This stock of nutritive material will sustain the life of the cutting during the first period after planting in the bed. As a consequence of this, notwithstanding the hot weather in July, the leaves of the cutting do not perish, and this is observed in the majority of pear varieties on which I am at present conducting the work refered to. As regards varieties of apple, with rare exceptions the whole process is limited to the formation of the callus, and cuttings with this callus, on being planted in the bed, lose their leaves and take root in the following summer. The cuttings are made and planted in beds five to seven weeks from the time the tubes were set, at one's own discretion. With cuttings from the second vegetative generation, i.e., when rooting cuttings not from seedlings but from specimens previously rooted by cutting, the entire process of development of the roots takes place much more easily and quickly. Evidently, the plant, in adapting itself to this operation, develops the ability to root more easily. Some varieties of pears, for example, seedlings of the well-known Olivier de Serres (see Fig. 47), manage to give in one summer two vegetative generations of rooting cuttings (see Fig. 48). In this way, it is easy to root branches taken from the crown of an adult tree with fruit buds and have low fruit trees of the old varieties with their own roots. This method of rooting, when it is fully worked out methodologically and technically, promises to cause a veritable revolution in the art of fruit growing in the future. In the present case we will have to wait a much shorter period for the fruit trees to begin to bear than in the case of grafted trees. In conclusion I must say that by way of experiment I cut and planted in the bed several cuttings from a pear with one callus even before the roots developed. True, the leaves of the cuttings suffered somewhat when they were planted in the bed; nevertheless, the cuttings will probably stand the operation well and in the spring will begin to develop roots, and then, perhaps it will be possible to dispense with the glass tube and water, and it will be only necessary to cover the ringed part of the cutting with the slit part of the rubber tube, which will be tied tightly to the bark above and below the bare part by tying it with cotton thread and smearing the slit in the tube with liquid grafting wax.

The cutting is made and planted in the bed six to eight weeks after the cuttings tube is fixed to the shoot.

Fig. 46. Formation of roots in tube and thickening of cuttings above tube Fig. 47. Cutting of hybrid seedling of Olivier de Serres pears with roots formed in tube Fig. 48. Detached cutting with roots formed in tube

CybeRose note: I think this technique could be used in breeding to increase seed set in difficult crosses, and to help overcome incompatibility. It might also be used to feed colchicine into woody plants to produce polyploids by inducing them to give unreduced ova and pollen.