RHIZOCARPE^E 23 



hardening of mucilage derived from the disorganisation and deliques- 

 cence of a portion of the contents of the sporange. The female prothal- 

 lium is formed within the apical papilla of the megaspore, and is 

 exposed by the bursting of the enveloping epispore. It never completely 

 frees itself from the megaspore, and is usually altogether destitute of 

 chlorophyll. It bears one or more archegones, differing from one 

 another in smaller points of structure in the different genera. The 

 microspores do not give birth to a male prothallium, nor even to 

 antherids, in the sense in which the terms are employed elsewhere in 



A 



FIG. 7. Salvinia natans L. A and B natural size, the latter with two aerial leaves and sub- 

 merged fertile leaves ; C, two sporocarps, slightly magnified and diagrammatic, one con- 

 taining a few megasporanges, the other a large number of microsporanges ; Z>, section of 

 empty sporocarp, slightly magnified. (After Luerssen.) 



Vascular Cryptogams ; the contents divide more or less directly into the 

 parent-cells of the antherozoids, which, accompanied by peculiar vesicles 

 attached to them, reach and impregnate the oosphere contained in the 

 central cell of the archegone. 



The external form of the sporophyte or non- sexual generation varies 

 widely in the different genera. The growth of both stem and root is 

 always the result of successive divisions from a single apical cell. The 

 stem is extremely abbreviated in Salvinia (Schreb.) and Azolla (Lam.) ; 

 procumbent and creeping in Marsilea(L.)andPilularia(L.). It is traversed 



