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 
