FILICALES 



341 



are absent (Fig. 15, p. 26). The whole body is thus capable of an inde- 

 pendent physiological existence, nourishing itself by absorption from 

 the soil, and by photo-synthesis (Fig. 283). But there is a large 

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



FIG. 282. 



Successive stages in germination of the spores of Nephrodium Filix-mas, to form 

 the prothallus. (After Kny.) 



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

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

 adapted for life on land, and more immediately dependent on moisture. 



The prothallus thus constituted is capable in some cases of vegeta- 

 tive propagation by " gemmae." But this gametophytic budding is 

 less common here than in the Bryophytes. 



The dependence on moisture is still more obvious in the behaviour 

 of the sexual organs which the prothallus bears. These are male and 

 female, and they may be found on the same prothallus (Fig. 283), or 



