FILK'AI.KS 



490 



cells divide by walls parallel to the flattened 3urfa md thu 



massive central cushion is formed. The mature cells are thin-walled, 

 with a peripheral film of protoplasm surrounding a central vacuole, 

 and embedding the nucleus and numerous chloroplasts : intercellular 

 spaces are absent (Fig. 19, p. u). The whole body is thus capablt 



Fig. 391. 



Successive stages in germination of the spores of Dryopteris Filix-mas, to forni 



the prothallus. (After Kuy.) 



an independent physiological existence, nourishing itselt by absorption 

 from the soil, and by photo-synthesis (Fig. 392). But there is a large 

 proportion of surface to bulk, and no serious resistance is ottered to 

 the evaporation of water from it in dry air. Comparing t he prothallus 

 with the Fern-Plant as regards the water-relation, it is plainly 

 adapted for life on land, and more immediately dependent on 

 moisture. 



The prothallus thus constituted is capable in some of 



