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TEXTBOOK OF BOTANY 



in Figure 48, by a circle with two main divisions. The 

 formation of spores by the asexual generation of the moss 

 results in a rapid increase in the number of plants as well as 



in a wide distribu- 

 tion of the species. 

 Something of this 

 sort seems to be 

 necessary, for the 

 moss can produce 

 only a small num- 

 ber of eggs, which 

 are confined within 

 the archegones and 

 whose fertilization is 

 not at all certain. 

 So, if the moss de- 

 pended entirely upon 

 sexual reproduction, 

 the chances for its 

 continued existence 

 would be comparatively slight. The occurrence of two very 

 different generations in the life of the moss is not unlike 

 what happens in the case of the bread mold, whose zygote 

 develops into a small plant quite different from the one that 

 produced the gametes ; and this small plant in turn bears 

 spores, each of which may grow into a plant that produces 

 gametes. 



123. Other Mosses. — There are about eleven thousand known 

 species of mosses, most of them very similar in their life histories to 

 the one that we have studied. Among our common and larger mosses 

 are the bird's wheat or pigeon wheat mosses and the tree moss. A very 

 important family is that of the peat mosses which grow in great num- 

 bers in peat bogs. Peat mosses live through the winter by means 

 of branches that start near the upper end of each plant ; these 

 branches live and grow the next year, while the older parts die. In 

 this way the plants live and grow, it may be for centuries, the older 



Fig. 48. — Diagram illustrating the life 

 cycle of a moss. 



