[Chap. XXXIII SEXUAL REPRODUCTION IN FLOWERING PLANTS 375 



through the style into the ovulary and finally to the ovule (Fig. 167). 

 This distance in most plants is short; but in the style of corn, which is 

 the silk, the pollen tube must often elongate more than a foot before 



Fig. 166. Stages in the development of an ovule and a young seed ot pepper. 

 A-D, formation of four megaspores (m) from a megaspore mother cell (mm) in 

 a young ovule; E, disintegration of three of the megaspores; F-I, development 

 of an 8-nucleate embryo sac from one of the megaspores, a fusion nucleus 

 is formed by the fusion of the two nuclei near the center of the sac, only a 

 little of the surrounding ovule tissue is represented; J, fertilization (f) and triple 

 fusion (tf); K, zygote (z) and triple-fusion nucleus (tfn); L, early stages in 

 the development of the embryo and endosperm of the seed. After H. L. Cochran, 

 Journal of Agricultural Research, with some modification. 



it penetrates the ovule. The direction of its growth is influenced by 

 chemical conditions within the pistil. A part of the distance it is grow- 

 ing in channels and intercellular spaces. Resistance to its growth 

 between closely packed cells is decreased by enzymes which bring 

 about softening of the tissues through which the tube grows. During the 

 growth of the tube, the nuclei are near the growing end. The pollen 



