38o 



SPOROPHYLLS OF ANGIOSPERMS 



rangia in which the microspores originate in fours as in the 

 preceding groups (Fig. 261 A, 3, 4). At maturity, the two 

 sporangia on each side of the anther usually merge into one 

 cavity, owing to the breaking clown of the intervening tissue. 

 The anther opens in a variety of ways, as by slits and pores, 

 permitting the scattering of the spores (Fig. 261^4, 3). The 



FIG. 2618. Megasporophyll and megasporangium: I, megasporophyll of 

 buttercup s, stigma; st, style; o, ovary. 2, longitudinal section of mega- 

 sporophyll mg, megasporangium; m, megaspore, the mother cell having 

 formed four spores in series, but the end one only develops; i, integument; 

 mi, micropyle. 



microsporophylls are often externally quite suggestive of those 

 noted in certain of the Pinales, but the megasporophylls are 

 essentially different from any other group considered, in that 

 the sporangia are inclosed in a cavity formed in the sporophyll. 

 This peculiarity is one of the important characteristics of the 

 angiosperms, as the name indicates. The megasporophyll, often 

 termed the pistil or carpel, is usually a rather elongated, flask- 

 shaped organ with a hollow swollen base and consists of a stigma, 

 style and ovary (Fig. 261 B, i) within which are produced the 

 megasporangia or ovules. Such a structure would result if the 

 edges of the leaf-like megasporophylls of previous groups were 

 inrolled so as to form a closed organ. The megaspores originate 



