16 



MORPHOLOGY OP SPERMATOPHYTES 



The first indication of a megasporangium is the differentia- 

 tion of a group of sporogenous cells immediately beneath the 

 epidermis. It is not a hypodermal plate, as in the microsporan- 

 gium, but a hypodermal mass of considerable extent. Whether 

 this group represents the archesporium, or whether it can be 

 traced back to a few-celled or even to a one-celled archesporium, 

 is still in doubt. Our impression is that there is a many-celled 

 archesporium. Following the differentiation of sporogenous 

 tissue, the exterior sterile cells begin to divide rapidly, organ- 

 izing the large sterile apical region of the nucellus. About this 

 there develops a very thick integument with a long and narrow 

 micropyle. 



By means of this development of the exterior sterile tissue 

 the sporogenous tissue becomes deeply placed in the nucellus, 



FIG. IS. Dioon edule, sectional view of strobilus represented in Fig. 12. 



appearing almost at its very base. In the sporogenous tissue 

 usually one centrally placed cell shows its selection for func- 

 tioning by enlarging at the expense of adjacent cells. From its 

 subsequent behavior it seems that this enlarging cell is the 



