322 



ELEMENTARY BIOLOGY 



thrown out of the opened top. When one of these spores alights 

 upon a moist spot, it absorbs water, and the protoplasm breaks out 

 on one side ; it then proceeds to develop into the next generation. 



Here again we must notice that the new plant developed from the 

 spore is not at all like the parent plant ; that is, the plant which 



produced the spores. 

 At first there is a 

 very delicate, green, 

 branching thread, re- 

 sembling some of the 

 green algae found in 

 water. In a short 

 time a clump of cells, 

 or a bud, appears at 

 some point along this 

 branching thread, and 

 from this develops 

 the leafy stalk that 

 we recognize as moss, 

 and some colorless, 

 hairlike threads that 

 look very much like 

 root hairs. 



The leafy moss 

 plant, bearing gamete 

 organs at the top, 

 is called a gameto- 

 phyte, which means 

 a gamete plant. The 

 leafless plant, con- 

 sisting of stalk and 

 capsule, together with the attachment to the parent, is called the 

 sporophyte\ that is, spore plant. By following the history of a 

 number of generations of moss we may see that there is a regular 

 alternation of gametophyte and sporophyte. This is illustrated in 

 the diagram (Fig. 149). 



374. Life history of a fern. In the ferns the spores are produced 

 on the underside of the leaves (see Fig. 127, p. 294). The spore gives 

 rise to a little plate of chlorophyl-bearing cells, sometimes no larger 



5 ( X 80) « ( X 10) 



Fig. 150. Reproduction in fern 



X 300) 



The gamete-bearing plant, <?, of the fern, called a. /'j-othallus, 

 is a flat plate of cells, with hairlike roots on the undersUr- 

 face. Flask-shaped organs, b, each bearing a single egg 

 cell, are embedded on the undersurface, near the notch, 

 with the mouth pointing downward and backward. Near 

 the small end of the prothallus, on the undersurface, are 

 the organs, c, bearing the male gametes. These are dis- 

 charged into the water, and swim about freely, finding their 

 way into the egg organ, where fertilization takes place 



