June, 1933] Pollination and Fruit Setting in the Apple 7 



Fig. 1 shows just how a leaf or shoot bud looks when cross-sectioned and 

 observed under the microscope. The hard outer scales enclose embryonic 

 hairs, leaves and leaf primordia. The growing tip located in the center has 

 a smooth, rounded surface. All leaf and flower buds in the first stage of 

 development show this appearance. 



After the first of July in New Hampshire, some of the buds on trees of 

 bearing age may show a change in the character of this central growing 

 point. Instead of remaining nicely rounded, the outline of the growing tip 

 becomes marked by angular projections. These elongate, so that after a 

 period of some three weeks, the buds have changed in appearance to that 

 noted in Fig. 2. Here the rudiments of the various flowers of the cluster 

 have been formed. Fig. 3 explains the parts and their regular succession. 

 The first prominences to appear are those of the outermost part or calyx ; 

 those of the pistil and ovules are last. 



Under favorable conditions the flower buds continue to develop slowly 



Fig. 3. Illustrating the development of the flower bud cluster. Bald- 

 win, March 9, 1933 (25x). A. Terminal bud of the cluster. B. Lateral 

 buds of the cluster, a. Primordia of calyx or sepals, b. Primordia of 

 petals, c. Primordia of stamens, d. Primordia of pistil, e. Cavity 

 which eventuallj' becomes the ovary with its contents — ovules, etc. 



through fall and winter. During April the primordia rapidly complete their 

 development into calyx, petals, stamens and ovary. Then in May warm 

 weather brings rapid growth and swelling of the flower buds. They subse- 

 quently burst into bloom, with matin-e pollen and ovules. 



Much can happen to prevent many or all of these embryonic flower buds 

 from reaching the mature stage. Factors that strongly inhibit fruit or 

 flower-bud formation are: 1. A heavy set' of fruit such as may occur espe- 

 cially in biennial bearers like Baldwin, Wagener, and Wealthy. 2. Heavy 

 shading, as from foliage of an extra-vigorous tree. 3. Cool w^eather or 



