FECUNDATION IN PLUM TREES
Dorsey, who studied the phenomenon of the caducity of blossom and young nuclei in plum trees, distinguishes three stages of this falling off of the nuclei.
The first one occurs during the blooming time; part of the blossoms fall off - those the styles and stigmata of which are withered. With those remaining on the tree the ovary of the pistil enlarges but soon becomes yellow and falls off too. These are the non-fertilized nuclei at which the zygote has not developed. The falling off takes place a fortnight after the pollination and the duration of this period is variable. On the tree there remain the fertilized nuclei and these develop quite quickly.
During the period of lignification of the stone their growth slackens only to increase again afterwards up to the perfect maturity of the fruit. During the period of the slackened growth the third falling off takes place, called "the June dropping", caused by an unequal supply of nutrient to the fruit. This June dropping constitutes a critical period for the development of the fruit, the period in which, according to weather conditions and the level of nutrient supply for the nuclei, the effect of the crops is being decided.
It has been stated that if the blossoming had been feeble or the precedent caducity intense, i.e. in both cases where there only remained few nuclei on the tree, this third falling off shows poorly.
In this period the embryo is not well developed yet.