290 



POMOLOGY 



nucleus and the other the generative nucleus. When the 

 pollen-grain germinates the latter nucleus divides, forming 

 two sperm or male nuclei. 



As the pollen-tube grows down the style of the pistil, the 

 male nuclei as well as the tube nucleus continue to approach 

 the embiyo sac in which are the ovules. Here the tip of the 

 tube enters the micropyl and dis- 

 charges the two nuclei into the em- 

 bryo sac so that fusion may take 

 place, one with the egg or female 

 nucleus and the 

 other with the 

 primaiy 



pericarp^_^ 



pollen tube 



synergids 



e^g nucleus 



nucellus 



embryo sac - - ' ' 



polar nuclei*-' 



anti podals -^"-'^ 



Fig. 36. — Diagram of a simple pistil as seen in 

 lengthwise section, showing a single ovule 

 just prior to fertilization. 



, outer Integument 

 sperm nucleus, inner Integumen 

 Hence it is seen 

 that two ferti- 

 lizations take 

 place, one hav- 

 ing to do with 

 the origin of a 

 new seed (ovule) 

 and the other 

 with the devel- 

 opment of the endosperm or food-storage tissue surrounding 

 the germ within the seed. As is well known from a study 

 of an immediate cross between field and sweet com, there 

 is an effect on the endosperm of the first or immediate 

 generation. This effect may be seen in the condition of the 

 kernel, i. e., when it is wrinkled or smooth or in the color 

 of the endosperm or in both. 



In a study of sterility of the common fruits (as well as 

 many other plants), it will be seen that not infrequently 

 the endosperm will develop but the embryo will perish, a 

 phenomenon termed embiyo abortion. (Fig. 36.) 



