DEVELOPMENT OF PLANTS 



251 



carrying the plant over unfavorable conditions for growth. In 

 other cases the spores have thin walls and germinate at once. 

 The advantage of the transference of the resting stage from a 

 single gametospore to the numerous spores derived from the 

 gametospore is manifest. 



(d) Germination of the Spore. The germination of the spore 

 is usually indicated by the formation of chlorophyll, and this is 



FIG. 184. Germination of the spores: A, spore. B, first division of the 

 germ tube. C, early form of the thallus, due to the formation and subse- 

 quent divisions of an apical cell. 



followed by the rupture of the outer spore coat and the protru- 

 sion of the inner as a delicate papilla or germ tube (Fig. 184). 

 Usually from this tube a small, hair-like outgrowth is soon 

 formed which penetrates the soil as the first rhizoid. The germ 

 tube continues to elongate and often forms a chain of cells by 

 successive transverse divisions, but eventually by oblique divisions 

 an apical cell is formed that develops the 'characteristic thallus 

 (Fig. 184, C). Thus we arrive again at the starting point in 

 the life history of these simple plants. 



(e) Noteworthy Departures in the Life History. It should 

 be stated that the gametophyte of certain species of the Marchan- 

 tiales may live for long periods without producing the gametes. 

 In fact, it frequently multiplies by means of buds and branches 

 which become detached and grow directly into new plants. How- 



