344 



REPRODUCTION IN PLANTS 



stages in each microscopic section. In each spore mother- 

 cell the chromatin net resolves itself into chromosome 

 threads. These then conjugate side by side. The paired 

 chromosomes next shorten and thicken. By the time 

 they are mature a spindle has been formed, which in 

 plants has blunt poles and lacks centrosomes such as are 

 always present in animals. Each chromosome pair has 



^ <9 



V 



Fio. 06. — Cell Division and Reduction Compared. Cell division 

 occurs rofrularly in growth, its essential feature is the longitudinal 

 splitting of each individual chromosome so that one-half of each 

 goes to each pole of the spindle and thus provides that the two 

 new cells shall be exactly like each other and exactly like the one 

 from which they have arisen. 



In reduction division the members of each chromosome pair, 

 first join side by aide and then arrange them.selves on the spindle in 

 such a way that one goes to each pole, thus segregating them from 

 one another. Since the pairs are arranged on the spindle in a chance 

 manner it follows that this not only reduces the number of chromo- 

 .somes that go to the spores but it also provides the means by which 

 new assortments arise so that the spores produced by a plant will 

 contain all the pa<»ible assortments of chromosomes. 



