280 



Science of Plant Life 



when mature produce gametes egg and sperm cells in 

 special organs at the stem tips. The sperms are swimming 



FIG. 165. A moss plant (Mnium). is a vegetative branch, B a branch that produces 

 eggs, and A a branch that produces sperms. After fertilization, an upright stalk bear- 

 ing a spore case (C) develops from the egg. A ' is a longitudinal section of a female 

 branch, showing three egg cells in the cases in which they are produced ; B' is a section 

 of a male branch, showing three of the organs that produce the sperms. 



cells much like those of algae. As they cannot reach the egg 

 cells except by swimming, fertilization takes place only when 

 the moss is wet. When the sperm unites with the egg, it 

 forms an oospore. 



Asexual reproduction. The oospore germinates while still 

 on top of the parent stem, and produces a long, stalklike body. 

 The base of this body grows downward into the parent stem 

 and draws water and nourishment from it. At the top of 

 the stalk a sporangium or capsule develops which contains 

 asexual spores. The stalk and sporangium live parasitically 

 on the green, leafy moss plant and are a distinct stage in the 

 life of the plant. 



