422 



BOTANY. 



532. Fertilization. Fertilization takes place as follows : 

 The pollen grain, resting upon the moist surface of the 

 stigma, absorbs moisture and germinates, sending out a tube 

 which penetrates the soft tissues of the stigma and style. 

 finally reaching the cavity of the ovary, where it enters the 

 micropyle of an ovule (Fig. 307, A}. Here it comes in con- 

 tact with the apex of the ovule body, through whose tissues 

 it forces its way until it reaches the embryo sac ; in some 



cases, however, the 

 embryo sac has grown 

 out through the apex 

 of the ovule body 

 into, and occasionally 

 through the micro- 

 pyle, thus meeting the 

 pollen - tube. T h e 

 transfer of the con- 

 tents of the pollen- 

 tube to the germ-cell 

 has never been ob- 

 served, but doubtless 

 it takes place by diffu- 

 sion through the pol- 



leu-tube and embryo 



the placenta ; ?, the raphe, swollen at this point fa, cop Tlip fir<sf VPII li- 

 the outer coat of the ovule ; i, the inner ;, the pol- SaC ' Liie llrst 1( 



licropyfe ; e, .em- o f fertilization is the 



Pig. 307. A, a longitudinal nctionof the anatro- 

 pous ovule of Viola tricolor, after fertilization, pi, 



raphe, swollen at this point ; a, 



ovule ; i, the in 



Jen-tube which has entered the mi 

 bryo sac, with the very young embryo at the micro- 

 pylar end, and numerous free endosperm cells at the formation of a Wall 01 

 other. S, apex of embryo sac. e (much more mag , 



nified) ; eb, very young embryo of two cells, support- C6liUl086 ai'OUnu the 

 ed by a two-celled suspensor. C, the same, further ,, . , , , 



advanced. All the figures highly magnified.-After germ-cell ; the latter 



soon divides trans- 

 versely one or more times, and thus gives rise to a row of 

 cells, the suspensor, at the free extremity of which a rudi- 

 mentary embryo is soon formed by the fission of cells in 

 three planes (Fig. 307). Simultaneously with the foregoing 



ized by Insects ; " " The Effects of Cross and Self-Fertilization in the 

 Vegetable Kingdom ; " " The Different Forms of Flowers on Plants of 

 the Same Species." Also Lubbock's " British Wild Flowers Considered 

 in Relation to Insects," and Dr. Gray's " How Plants Behave." 



