THE CLUB-MOSSES 



547 



Fig. 376. — Martin's Selaginella (Selaginella Martensii, Selaginella Family, 

 Selaginellacece). Germination of macrospore i^i), cut vertically, 

 showing the female gametophyte protruding from the ruptured spore- 

 wall (spm) and exposing an unfertilized archegonium (ar), but still 

 enclosing two embryos {ernb^, emb-) which have been pushed down into 

 the nutritive prothallus (/)/) by their suspensors {et, et). (Pfeffer.) — 

 Native home, Mexico; much cultivated. 



Fig. 377. — Martin's Selaginella. Embryo (M"). cut vertically to show its 

 suspensor (et), root (w), leaves {bl, bl), ligules (lig, lig), and tip of stem 

 (st). (Pfeffer.) 



projection (lig) termed a Ugule,^ arises, which, by secreting mucilage, 

 serves to l^eep the tender terminal organs from drying. 



The formation of macrospores that begin to germinate while 

 still within the sporangium, marks a most important advance in the 

 care of offspring ; for by this means not onh' are the chances of cross- 

 fertilization increased, but the embryo is afforded more protection, 

 and the young plantlet can be provided with a larger quantity of 

 promptly available food while preparing for independent life. Just 

 one step further is needed as we shall see, to attain the high develop- 

 ment of parental care achieved by seed-plants. A similar differen- 

 tiation of the spores and sporangia into male and female is found 

 also in certain types of Filicinae, and in extinct Equisetinse. 



As with scoiiring-rushes and ferns, so with the club-moss 

 class, the modern species but feebly represent their kin of 

 the coal age. These include giant lycopods such as Lepido- 

 dendron (Fig. 278, page 301) and Sigiilaria (Fig. 277, page 299) 

 with much-branched trunks ten meters or more in height and 

 often a meter in thickness, bearing cones as large as those 

 of a pine tree, and forming extensive forests. 



1 Lig'ule < L. Ugula, a little tongue. 



