THE REPRODUCTIVE STRUCTURES 99 



in size and finally becomes the largest nucleus ever 

 observed in plants, having — in extreme cases — a diam- 

 eter of one-fiftieth of an inch. This is the nucleus of 

 the egg. Practically, the central cell is an egg, but we 

 do not use the term egg until the division has occurred 

 which results in the formation of the egg nucleus and 

 the ventral-canal nucleus (Fig. 44). Immediately after 

 the division the egg nucleus moves down into the central 

 part of the egg, while the ventral-canal nucleus dis- 

 organizes and disappears (Fig. 45). 



The egg is now ready for fertilization. Although 

 numerous archegonium initials may be formed, only a 

 few finally produce eggs, the number of eggs usually 

 ranging from four to ten. Microcycas, which was 

 investigated by Caldwell, is very exceptional in this 

 respect, having scores and sometimes hundreds of eggs. 



