Fig. 131. The Vegetativnaya pear tree
|a) one-year-old shoot; b) tip of one-year-old shoot with group of leaves from shostalks a vegetative pear is formed; c) vegetative fruit with rosette of remaining leaves in upper hollow; d) lower part of trunk of scion; e) excrescence on stock|
In addition to the varieties described above, I find it absolutely necessary to give an account of an interesting variety of pear that has been found in the mountains of North Caucasus.
The Vegetativnaya pear is a matter of outstanding world interest because in the course of the vegetative period it produces three cropstwo by sexual means and one by vegetative means, which is never observed in other perennial fruit plants.
In the summer of 1931 I sent my immediate assistant, Pavel Nikanorovich Yakoviev, who has thoroughly studied and fully understands the work of hybridization, to get this pear, and soon after he brought me all the material and precise information, collected where this pear was foundin the mountains of North Caucasusthat interested me.
It was ascertained that in the spring, like all other varieties, this pear blooms and bears fruit of medium size and of fairly good flavour. After the fruit ripens, in the first half of July, the tree blooms a second time and simultaneously, the buds on the young shoot give rise to small stalklike formations which, in their turn, bear several buds at the tips crowded close together; from these buds leaves begin to develop.
As these leaves grow, their petioles gradually and simultaneously begin to swell, and by the end of August and beginning of September, when the pears from the second blooming are already ripening, the fruit that was formed vegetatively from the petioles also acquires pear shape; and by this time the petioles are quite imperceptible, because it was from their simultaneous thickening on the fruit stalks that these fine pears, which for size and flavour cannot be distinguished from fruit that had set at blossoming, were formed.
The leaf blades of the petioles from which the "asexual" pears are formed do not disappear like the stalks; they remain in the place of the calyx, gracefully protruding from the top of the vegetative fruit in the form of a large bunch of rosettes (see Fig. 131).
A detailed inspection of the garden where this pear grows revealed that there were two specimens of this variety of pear at the place and both proved to be grafted, the scion looking somewhat thinner than the stock and having a large excrescence above the latter (such an excrescence is often found on grafted varieties of fruit trees which have a stock of an alien species).
In addition to cuttings from this vegetative pear, roots were also taken for the purpose of ascertaining the species of the stock on which this pear had been grafted, for the possibility was not precluded that all this mix-up in fruit bearing was due to the influence of the stock.
The cuttings from this exceptionally interesting pear were grafted on August 11, 1931, in our chief scientific department [the Plant-Breeding and Genetics Station], on to different species of stock: apple, pear, quince, mountain ash, service tree and hawthorn.
The excellent way in which the buds took to all kinds of stocks, which became evident already in September, reveals the enormous plasticity and adaptability of this pear in respect to joining easily with remote species.
It may be hoped that the Vegetativnaya pear will, in its turn, either by planting, or by hybridization with other, cultivated varieties of pears and with other species and genera of fruit plants, produce a number of excellent varieties that will be capable of bringing about a great improvement in socialist fruit growing.
The bulletins on the work of the experimental station will give reports on the results of the experiments made with the Vegetativnaya pear, and, in particular, on the correlative influence upon it of different species of stocks.