CYCADALES 



19 



III. THE GAMETOPHYTES 



THE FEMALE GAMETOPHYTE 



The gametophyte generation begins with the reduction divi- 

 sion of the enlarged mother cell which lies deeply imbedded in 

 the nucellus and surrounded by more or less sporogenous tissue 

 which does not function as such. According to Treub n and 

 Lang, 29 in Ceratozamia and Stangeria the transverse division 

 of the mother cell results in a row of three cells (Fig. 19), which 

 may be called potential megaspores, the lowest of which becomes 

 the functional megaspore. Whether this is true of all Cycads 

 or not remains to be seen. The 

 selected megaspore enlarges 

 rapidly at the expense of the 

 two functionless megaspores, 

 disorganizing them as well as 

 a varying amount of adjacent 

 tissue. The outer wall of the 

 megaspore is said to become cu- 

 tinized in Cycas, and this may 

 be true of other genera as well. 

 In any event, it suggests deriva- 

 tion from forms in which the 

 spores are discharged. 



The germination of the meg- 

 aspore and the development of 

 the female gametophyte was 

 first published in any detail by 



Warming, 8j 9 Cycas circinalis being the form studied. Addi- 

 tional incidental testimony has been given by Treub, 11 by 

 Ikeno 2S in his study of Cycas revoluta, and by Lang 29 in his 

 study of Stangeria pamdoxa. It is often stated in a general 

 way that the development of the endosperm resembles that in 

 Selaginella and Isoetes, but since our knowledge of the develop- 

 ment in these forms has been obtained by putting together 

 fragments of information, such a statement does not rep- 

 resent any very exact knowledge. Unpublished results ob- 

 tained by Miss F. M. Lyon with Selaginella show that some- 

 thing more than inference from fragments is needed. So far 



FIG. 19. Development of the megaspore : 

 A, Stangeria paradoxa, showing the 

 functional megaspore enlarging at the 

 expense of two functionless mega- 

 spores, x 250; i?, Ceratozamia longi- 

 folia, showing the three potential 

 megaspores, the lowest beginning to 

 enlarge, x 266. A, after LANG ; B, 

 after TREUB. 



