170 



SIGNIFICANCE OF SEX 



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). 



This tendency 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 smallness pro- 

 motes their movements through the water. The increase in the 

 size of the female gamete renders her movements more diffi- 

 cult, but the storage of food in this gamete provides for the 



Fig. 103. Features in the life history of Volvox: A, a colony which may 

 contain as many as 20,000 plants. The three central groups are young col- 

 onies which may arise by the repeated division of any of the plants. B, side 

 view of one of the plants showing the canal-like connections with the neigh- 

 boring plants. C, surface view of a plant with canals radiating out to the 

 adjoining plants. D, a plant enlarging and forming a single motionless female 

 gamete. E, a plant forming numerous small male gametes. F, male gametes 

 enlarged. 



better nourishment of the next generation. Finally the nourish- 

 ing function becomes so strongly developed that the female 

 ceases to move at all and remains protected in the mother cell. 

 Thus we see that sexuality arose among plants as the result of 



