i8o DIFFERENTIATION OF SEX 



the amount of nutriment which they receive. Consequently, 

 the gametes formed from them must also differ in size. It is 

 also possible that the mother plants may produce gametes of 

 different sizes because some divide a larger number of times than 

 others. The larger the number of divisions in a cell, the smaller 

 will be the gametes. It is interesting to note that these gametes 

 fuse quite regardless of their size, although there may be a slight 

 tendency for the small and more active gametes to fuse with 

 the larger and slower moving ones. Thus we have an illustra- 

 tion of the first appearance of the differentiation of sex although 

 the sexuality of the gametes is not thoroughly established. The 

 gametospore, resulting from the union of the gametes, develops 

 a thick cell wall, the contents assumes a reddish color and it 

 passes into a resting stage (Fig. 102, F). When conditions are 

 favorable, it germinates as shown in Fig. 102, G-H. In the 

 beautiful spherical colonies of Eudorina and Volvox (Fig. 103) 

 the differentiation of the gametes is complete. Certain cells 

 produce but one large female gamete that remains motionless 

 in the mother cell while other cells form numerous small motile 

 male gametes which are yellowish in color. In Volvox, over 

 200 male gametes may be formed from a single cell (Fig. 103, 

 D, E). Volvox also shows that the association of plants in 

 colonies resulted in an interdependence among the plants and 

 also in a specialization in the work performed by these plants. 

 Fig. 103, C, shows that the thousands of plants that make up the 

 colony are in communication with one another and they doubt- 

 less give and receive material in accordance with the needs of 

 the colony. Furthermore a few of the cells of the colony receive 

 more nourishment than the others and these cells increase in size, 

 divide and form new colonies as in Pandorina. Finally there is 

 to be noticed that certain cells function in the production of 

 gametes. So we see here in a simple way some of those speci- 

 alizations and distributions of labor that will appear as the most 

 characteristic features in higher forms. 



The tendency among the algae to form gametes of different 

 sizes is manifestly of great advantage. The great number of 

 male cells increases the chances of fusion of the gametes and their 



