LFCOPODIACE.E. 



403 



originally curved spirally round the central vacuole ; this latter, surrounded by a 

 fine membrane, not unfrequenlly remains attached to the posterior end of the 

 antherozoid after it has escaped, and is carried along by it. The movement does 

 not last longer than five minutes in the antherozoids of Isoetes, in Selaginella from 

 one-half to three-quarters of an hour. From the commencement of germination 

 till the complete maturity of the antherozoids there is, in Isoetes, an interval of 

 about three weeks; the same period from the dissemination of the spores is neces- 

 sary in Selaginella. 



The JMacrosporcs produce the female prothallium, which is an endogenous struc- 



fV^:^ 



Fig. 303.— Germination of Selaginella (after Pfeffer) ; /—///, S. Martensii, A—D, S. caulescens; I longitudinal section of a 

 macrospore filled with the prothalliinn and ' endosperm,* d the diaphragm, ee' two embryos in process of formation ; //a young 

 archegoniuni not yet open ; /// an archegonium with the oospore fertilised and divided once ; A a microspore showing the 

 primordial cells ; B C different views of these divisions ; D the mother-cells of the antherozoids in the perfect anther- 

 idium. 



ture in a still higher degree even than is the case with Rhizocarps. In this respect 

 and in the mode of its development, it shows a still greater resemblance to the tissue 

 that fills up the embryo-sac of Gymnosperms, and even of Angiosperms. In Isoetes 

 the cavity begins to be filled with cellular tissue a few weeks after the escape of the 

 macrospores from the decaying macrosporangium ; the cells of this tissue are all at 

 first still naked (without cell-wall) : they appear to become enclosed in firm cell- 

 walls only when the whole cavity of the endospore is filled with them (Fig. 302). 

 In the meantime the endospore thickens, becomes differentiated into layers, and 



D d 2 



