320 



SELAGINELLA 



to a terrestrial existence. Associated with the last-named feature 

 we see the differentiation of proper conducting tissue and of 

 true roots. There is, moreover, a marked tendency towards 



FIG. 182. Selaginella, prothallia and embryology, a, .front view, and 

 b, vertical section of mature megaspore with female prothallus ; c, older 

 embryo ; d, spermatozoid ; e, archegonium in longitudinal section ; 

 /, microspore with contained male prothallus ; g, young plant still 

 attached to the megaspore (sp.). ar., archegonia ; e., embryo (in b) ', 

 /., large-celled nutritive tissue (in b) ; ft., foot (in c) ; I., leaves of 

 embryo ; o., egg (in e) ; p, prothallus ; r., radicle ; S., suspensor ; Sp., 

 coat of megaspore. (a, e, and g after Bruchman ; d after Belajeff ; 

 remainder after Pfeffer.) 



division of labour, on the one hand between vegetative and 

 reproductive leaves, on the other between the prothalli. In 

 the Ferns all the latter are alike and bear both kinds of sexual 

 organs, although there are occasional exceptions when the con- 



