240 



STRUCTURE AND LIFE HISTORIES 



as the gametes are set free fertilization takes place, pro- 

 ducing a fertilized egg, with, of course, the double or diploid 

 number of chromosomes. Every cell of the sporeling, 

 resulting from the germination of the oosperm, and every 

 cell of the mature plant into which it develops, possesses 

 the double number, up to the first two divisions of the 



■•■■^^ 1 Stage 



Fig. 176. — Diagram of life-cycle of Ascophyllum nodosum. 



young gametangia, when reduction gives rise to gameto- 

 phytic cells. The fusion of these — egg with sperm — in 

 fertilization restores the double or sporophytic number 

 and so on in cycle after cycle (Fig. 176). 



225. Diagram of Life History. — The successive steps in 

 the life cycle of Ascophyllum may be briefly summarized 

 as follows: 



