l66 STRUCTURE AND LIFE HISTORIES 



tube, the germ-tube, or protonenia (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 



