CHAPTER XIX 



FERTILIZATION AND POLLINATION 



259. FERTILIZATION. Seeds result from the union of two 

 elements or parts. One of these elements, a nucleus of a 

 plant cell, is borne in the pollen-grain. The other element, 

 an egg-cell, is borne in the ovary. The pollen -grain falls 

 on the stigma (Fig. 202). It absorbs the juices exuded 

 by the stigma and grows by sending out a tube (Fig. 203). 

 This tube grows downward through the style, absorbing 

 food as it goes, and finally reaches the egg -cell in the 

 interior of an ovule in the ovary, and fertilization, or 

 union of the two nuclei, takes place. The ovule then 

 ripens into a seed. The growth of the pollen -tube is 

 often spoken of as germination of the pollen, but it is not 

 germination in the sense in which the word is used when 



speaking of seeds. 



260. Better seeds that is, those 

 which produce stronger and more 

 fruitful plants usually result 

 when the pollen comes from another 

 flower. Fertilization effected be- 

 tween different flowers is cross- 

 fertilization ; that resulting from 

 the application of pollen to pis- 

 tils in the same flower is close- 

 fertilization or self-fertilization. 

 It will be seen that the cross -ferti- 

 lization relationship may be of many degrees between two 

 flowers in the same cluster, between those in different clus- 

 ters on the same branch, between those on different plants. 



(128) 



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202. B, pollen of plum escaping 

 from anther. A , pollen ger- 

 minating on the stigma. 

 Enlarged. 



