3 88 



STRUCTURE AND LIFE HISTORIES 



gonium, after the first division of the egg, is a suspensor, 

 but becomes much longer than in Lycopodium, and 

 thrusts the developing embryo deep down among the 

 nourishing cells of the gametophyte. By the possession 

 of a suspensor the Lycopodiales and Selaginellales are 

 distinguished from the Pteridophytes and Catamites. 



The embryo does not cease growth, and pass through a 

 resting period, but continues to develop, until its root and 

 shoot, with two cotyledons, emerge from the prothallus, 



FIG. 284. Diagram of life-cycle of Selaginella. (Modified from J. H. 



Schaffner.) 



and the young sporophyte gradually becomes established 

 as an independent, green plant (Fig. 284). It is only after 

 the development of a vigorous leafy shoot, with chloro- 

 phyll apparatus, capable of elaborating an abundance of 

 food, that the strobilus is organized with its axis and 

 green sporophylls. 



