102 



MANUAL OF BOTANY 



chambers, and usually a single central stele. The structure of 

 the rhizophore resembles that of the root. 



The sporangia are developed much as in L^-copodium ; the 

 macrosporangia differ from the microsporangia in the number 

 of divisions that take place in the cells of the archesporium. 

 In the latter case many mother-cells are produced, each giving 

 rise to four tetrahedral microspores ; in the former case not so 

 man}^ are formed, and only one of them as a rule divides to 

 form spores. Hence the mature macrosporangium contains four 

 macrospores. 



Fig. 019. 



Fi'j. 919. Section of stem of Bdwjbvdhi showing three steles, a, b, air chambers. 



The male gametophyte arises from the microspore, and is 

 very similar to that of Marsilea. The spore divides into two cells, 

 a small vegetative one at the apex, and a large basal one which 

 by repeated divisions produces a single antheridium, having a 

 wall enclosing the mother-cells of the antherozoids. The micro- 

 spore does not rupture until the antherozoids are developed. 



The germination of the macrospore gives rise to a prothal- 

 lium which is very largely endosporous. The spore contains a 



