The Hormone Content of the Seed in Relation to Endosperm Development and Fruit Drop in the Apple

Apple seeds at certain stages of development have been shown to contain a hormone which can be extracted with boiling water and which is active in stimulating the development of unpollinated tomato ovaries. Use has been made of this latter fact to detect and measure the amount of hormone present in the seeds at various stages of development, using the methods described in the previous paper (see pp. 19 to 31).

In the variety Beauty of Bath the appearance of the hormone in the seed at 25-30 days after petal-fall corresponded with the cessation of the post-blossom drop, and the disappearance of hormone from the seeds of nearly ripe apples was correlated with the occurrence of the pre-harvest drop. The seeds from “ June drop ” fruitlets of two other varieties contained much less hormone than those from fruitlets remaining attached to the tree, and from this and other evidence it is concluded that this hormone is concerned with the control of fruit drop. It appears to be produced in the endosperm tissue of the seed but not in the embryo. Although it will stimulate the development of tomato ovaries it apparently plays no direct part in initiating fruit growth in the apple. The presence of a second, as yet undetected, hormone with this function is postulated.