/ . 





^. 



o 





^i^ 



Chromatin network 

 in germ mother cell 



Chromatin in 

 thickened spireme 



Chromosomes Chromosomes at equator 



in pairs 



./ 





/ 



1 



Q 



Chromosome 

 pairs separate 



Chromosomes migrate 

 toward poles 



/ 



Chromosomes form 

 two new groups 



Two new nuclei 



THE FORMATION OF GERM CELLS 



In the formation of gametes in plants and animals, the chromosomes of each pair be- 

 come separated during one cell division. As a result, each germ cell finally has only 

 half the number of chromosomes present in the body cells of the species 



good healthy growth would not be sufficient to ensure seed. And they knew 

 that flowers would fail to produce seed unless some of the powdery or sticky 

 pollen, or flower-dust, gets onto a special part of the flower, the stigma (see 

 illustration, p. 399). Yet Aristotle and other great thinkers rejected the idea 

 that there could be "sex" in plants. 



It was difficult to think of sex in plants, first for the reason that we com- 

 monly associate maleness and femaleness with two distinct kinds of individuals 

 in most familiar animals. In addition, the familiar seed-bearing plants do not 

 directly bear eggs or sperms. Although the experience of the race had es- 

 tablished the fact that pollen somehow makes flowers capable of bearing 

 seeds, it was necessary to wait for the microscope before anybody could know 

 just what the connection is. So it came about that it was only about two 

 hundred and fifty years ago that anybody did know just what the pollen has 

 to do with the "setting" of seed. This was first worked out by a German 

 botanist and physician, Rudolph Jacob Camerarius (1665-1721), who reported 

 his discoveries in letters he wrote in 1694. 



If we assume that the union of two cells is the essential fact about sex, it is 

 interesting to note that some of the characteristics of the male and female 

 gametes appear to be repeated and enlarged, or even exaggerated, in the entire 

 organism. Maleness shows itself as movement, restlessness, a seeming drive to 

 go places. We may recognize femaleness in a certain inertness, or remaining 



389 



