1 66 STUCTRURE AND LIFE HISTORIES 



tube, the germ-tube, or protonema (first thread), begins 

 to develop. This process is germination. Shortly, near 

 the wall of the spore, a smaller, slender tube develops as 

 a branch of the germ-tube (Fig. 125 ). This is the first of 

 innumerable root-like bodies, or rhizoids, which will 

 help to hold the new plant firmly to the soil, and also serve 

 to take in water and dissolved mineral nutrients. 



152. The Prothallus. Before the germ- tube has greatly 

 enlarged, it becomes divided into two cells, and then, by 



FIG. 126. Prothallus of a fern. Archegonia on the (central) cushion, 

 near the notch; antheridia among the rhizoids, below. (After Margaret 

 C. Ferguson.) 



successive cell-divisions, into an increasing number. 

 Meanwhile chlorophyll bodies begin to appear, but never 

 in the rhizoids. The final product of these cell-divisions 

 and growth is a tiny, flat, green body, often (but not 

 always) heart-shaped, with a central portion, the cushion, 

 several cells thick, and a marginal part, the wings, of 



