2l8 



STRUCTURE AND LIFE HISTORIES 





1>^^ 





early stages of development the sporophyte ceases to grow 

 at the apex, and elongates only by the formation and 

 enlargement of new cells just above the foot {intercalary 

 growth). Around the base of the sporophyte there 

 develops from the tissue of the gametophyte a sheath, 

 but, in contrast with the mosses, no seta is formed. The 



appearance of the sporophytes, 

 as they appear in clusters, has 

 been aptly likened to tufts of 

 delicate blades of grass (Fig. 

 156). Spores are formed from 

 the cylindrical archesporium, 

 between outer and inner layers 

 of sterile tissue. The inner 

 thread-like layer is the colu- 

 mella (Fig. 156). Chlorophyll 

 develops in the sterile cells, and 

 intercellular spaces open to the 

 surface through true stomata 

 (Fig. 166). The sporophyte, 

 therefore, has the function of 

 photosynthesis, and if only a 

 root, or roots, would develop 

 from the basal portion, it could 

 well become established as an 

 independent plant. As it is, it can live only as long as 

 the gametophyte remains active, so as to maintain the 

 supply of water to the sporophyte. The columella serves 

 to conduct water up the sporophyte. 



199. Formation of Spores. — As in the mosses and 

 ferns, spores arise from spore-mother-cells by reducing 

 divisions (tetrad-formation). In Anthoceros they do 



Fig. 164. — Bryopteris fili- 

 cina, showing long shoots and 

 short shoots. The stolons at 

 the base, with reduced leaves, 

 serve not only in vegetative 

 propagation, but also to anchor 

 the plant. (After Goebel.) 



