264 



THE SPORE OF RICCIOCARPUS 



spore mother cells, form four spores each, as in the tetraspores 

 of the red algae (Fig. 183, D). The delicate walls of the cap- 

 sule break down as soon as the spores are matured, leaving them 

 free in the archegonium, and later they are set free by the decay 

 of the latter organ. These spores in some forms are provided 

 with thick walls and are, therefore, resting spores adapted to 

 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 thalhis, due to the formation and subse- 

 quent division of the 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 divi- 

 sions 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. 



