368 



SELAGINELLA 



small prothallus (prth), and a process of division also takes 

 place in the remaining contents (c) of the spore, producing a 

 large-celled tissue, the secondary prothallus. 



By the rupture of the double cell-wall of the megaspore, 



mi 



-*-- . FIG. 87. Reproduction and Development of Selaginella. 

 - A, diagrammatic vertical section of a cone consisting of an axis bear- 

 ing close-set sporophylls (sp. ph), on the bases of which microsporangia 

 (mi. spg) and megasporangia (mg. spg) are borne. 



B, section of a microspore, showing the outer coat (mi. sp), prothallial 

 cell (prth), and multicellular spermary (spy). 



C, vertical section of a megaspore, the wall of which (mg. sp) has been 

 burst by the growth of the prothallus (prth) : its cavity (c) contains a 

 large-celled tissue, the secondary prothallus : in the prothallus are three 

 ovaries (ovy), that to the left containing an ovum, that to the right an 

 embryo (emb) in the polyplast stage, and that in the centre an embryo 

 in the phyllula stage, showing stem-rudiment (st) and two cotyledons 

 (ct) : both embryos are provided with suspensors (dotted) (spst), and 

 have sunk into the secondary prothallus. 



(Altered from Sachs. ) 



the prothallus is exposed to the air, but it never protrudes 

 through the opening thus made, and is therefore, like the 



