REPRODUCTION 



187 



iiilieritaiico, which we shall later discuss. In this division the 

 chromosomes, as they make their appearance out of the nuclear 

 network, are grouped in pairs; and when division takes place, 

 the members of each pair separate, one going to one of the 

 newly formed nuclei and the other to the other. The splitting 



^ 





E F & 



Fig. 100. — Diagram of mitosis in a ordinary bodj^-cell. A, resting nucleus. 

 B and C, prophases. D, metaphase. E and F, telophases. G, new cells. The 

 separate chromosomes, each of which has an individuality of its own, are differ- 

 ently marked. It is evident that the chromatic material is divided exactly 

 evenly between the two daughter cells. {Modified from Sharp). 



of chromosomes which occurs in ordinary mitosis (Fig. 100), and 

 by which the chromosome number is maintained, does not occur 

 here, and the resulting daughter nuclei (and the gametes de- 

 rived from them) therefore contain only half the chromosome 

 number found in the ordinary body cells of the plant. Such a 

 division is accordingly known as a reduction division (Fig. 101). 

 When the gametes later unite in fertiUzation, each contributes its 

 quota of chromosomes, and in the fertilized egg the original chro- 

 mosome number is thus restored and then persists throughout 

 all the cells of the plant which develops therefrom. The essential 

 differences between these two types of division are shown in the 

 appended diagrams. 



Perianth. — The pistil occupies the center of the flower, with 

 the stamens in a circle around it; and outside of these, in turn, 

 is the 'perianth, composed typically of two circles of parts. The 

 inner one of these is the corolla or circle of petals. The petals are 

 flat, somewhat leaf-like structures, usually conspicuous in color 

 and rather delicate in texture, whose chief function is to attract 



