GERMINATION 25 
exposed to suitable conditions of moisture and temperature each spore may 
germinate: the outer coat bursts, and the inner protrudes and increases 
in size, cell-divisions appearing as the growth proceeds. The body which 
is thus produced is called the prothallus, and it may vary in its form 
according to .the circumstances. In average cases of not too crowded 
culture it usually takes first a short filamentous form, attached by one 
or more rhizoids to the soil (Fig. 9. 4): it then widens out at the tip 
Fic. 9. 
Germination of the spore in Mephrodium Filix-mas, and early stages of the prothallus. 
; : (After Kny.) 
to a spathula-like, and finally to a cordate form (Fig. 9. 5 and 6). This: 
is the usual type, but when. crowded closely together, the filamentous 
form may be longer retained, and prothalli are then of the type shown 
in. Fig. 11. 1. It is thus seen that the form of the prothallus is plastic, a 
fact which may be brought into further prominence by culture. under 
various conditions of lighting, etc. 
‘The body of the prothallus, exclusive of the downward growing rhizoids, 
consists of cells which are essentially alike, arranged at first in a single- 
layered sheet. This simple structure is maintained permanently by the 
