NATURE OF THE FERTILIZING PROCESS 



143 



177. Nature of the fertilizing process. The necessary feature 

 of the process of fertilization is the union of the essential contents 

 of two cells, especially the nuclei, to form a new one from which 

 the future plant is to spring. This kind of union also occurs in all 

 the lower plants (Chapters xx-xxxi), resulting in the formation of 

 a spore capable of growing into a complete plant like that which 



FIG. 156. Germination of the pollen grain of an angiosperm 



A, inner coat of the pollen grain distended by osmosis from contact with the moist 

 stigma, and protruding slightly at the point i; B, the pollen tube beginning 

 to form ; C, the pollen tube more elongated, with the tube nucleus t at its tip, 

 the generative cell g having begun to enter the tube ; D, the pollen tube still 

 farther elongated ; E, the division of the nucleus of the generative cell to form 

 the two sperm nuclei s\ and sz ; f\ the sperm cells Si and s% fully formed, 

 and the tube nucleus t breaking down ; G, the tube nucleus has disappeared, 

 and the sperm cells are about to be discharged near the tip of the pollen tube. 

 Somewhat diagrammatic and much magnified. After Bonnier and Sablon 



produced it. It is a sexual act and can be studied much better in 

 some of the algae, mosses, and ferns than in seed plants. 



178. Development of the embryo. After fertilization the 

 egg cell finally develops the embryo of the future seed. This 

 formation of the embryo is always a complicated process and 

 varies much in different groups of seed plants. Briefly stated, 



