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 



FIG. 9. 



Germination of the spore in Nephrodimn Filix-mas. and early stages of the prothallu.s. 



(After Kny.) 



to a spathula-like, and finally to a cordate form (Fig. 9. 5 and ft). This 

 is the usual type, but when crowded closely together, the filamentous 

 form may be longer retained, ai:d prothalli are then of the type shown 

 in Fig. ii. i. It is thus seen that the form of the protua'llus is elastic, a 

 fact which may be brought into further prominence by culturte 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 



