THE REPRODUCTIVE STRUCTURES 



lOI 



The male cone consists of an axis bearing numerous 

 modified leaves, called microsporophylls, which show 

 little or no trace of the pinnate 

 character of the leaves from 

 which they have been derived. 

 On the under surface the micro- 

 sporophylls bear numerous 

 microsporangia arranged in 

 groups called sori (Figs. 47-49). 



The grouping of sporangia 

 into sori is characteristic of 

 ferns, but the number in a 

 sorus is very much larger than 

 in cycads. In the more primi- 

 tive cycads, like Cycas and 

 Dioon, the predominant num- 

 bers in a sorus are the five's, 

 four's, and three's, while at the 

 other end of the series scarcely 

 any five's are found and four's 

 are scarce, the usual numbers 

 being the three's and two's. 

 Occasionally the sorus consists 

 of a single microsporangium. 

 The cycads show a steady 

 tendency to reduce the number 

 of microsporangia in a sorus. 



There is also a persistent 

 tendency to reduce the total 

 number of microsporangia on a 

 sporophyll. A large number of sporophylls of Cycas 

 circinalis and Dioon spinulosum, representing the more 



a^ 



Fig. 46. — Ccralozamia 

 mexicana: male cone; the 

 entire cone, with stalk, is 

 9 inches in length. 



