DEVELOPMENT OF PLANTS 



281 



spore mother cell, but in the Red Algae and Ricciocarpus a con- 

 siderable growth intervenes before the spore mother cells appear 

 and the reduction of the chromosomes takes place. In other 

 words, as we ascend the scale of plant life, the formation of the 

 spore mother cells and the reduction of the chromosomes is pre- 

 ceded by an ever-increasing growth of the gametospore. This 

 postponement in the formation of the spore mother cells, owing 

 to the larger and larger growth of the gametospore, will steadily 

 progress in the following studies. 



These simple liverworts, like Ricciocarpus, show very clearly 

 two phases or generations in their life history. The thallose 



Fig. 185. Diagram of the life history of Ricciocarpus. The upper por- 

 tion of the figure represents the sexual generation and the lower portion, 

 the asexual. The former generation begins with the formation of the spores, 

 sp, from the mother-cell and ends with the formation of the gametes, ^. The 

 asexual generation begins with the gametospore, gm, and ends with the spOre 

 mother cells, sm. 



plant is the gametophyte or sexual generation because it bears 

 sexual cells or gametes. The capsule is the sporophyte or asex- 

 ual generation because it can only produce spores. The gameto- 

 phyte begins with the spore and ends with the formation of the 

 , gametes. The sporophyte begins with the gametospore and ends 

 with the division of the spore mother cell (Fig. 185). It may 

 appear to you now as strange to regard the few cells of the cap- 

 sule, the majority of which become spore mother cells, as a plant. 

 But we shall directly see this microscopic plant assuming larger 

 proportions as a result of its better nourishment and the stimuli 

 to which it is exposed. It will form a larger and larger number 



