PTERIDOPHYTA 



227 



being turnip-shaped, cylindrical, flat, or irregularly bulbcnis. In Lycopo- 

 dium cernuum, a widespread tropical species, the prothallium is an erect 

 cylindrical body only 2 or 3 mm. long. It grows at the surface of the 

 ground and consists of a colorless basal portion buried in the soil and a 

 conspicuously lobed aerial crown that is green and bears the sex organs. 

 The lower portion produces rhizoids and contains an endophytic fungus. 

 The spores germinate promptly and the prothallium reaches maturity in a 



Fig. 183. Gametophyte of Lycopodiitm davatum. A, the entire gametophyte, tvnce 

 natural .size; 5, longitudinal .section with antheridia in center and archegonia to the left 

 and right, X 20. In the embryo, shown in outline, a young .shoot has developed above, a 

 young root to the right, and a large foot below and to the left. The shaded cells in the 

 lower portion of the prothallium contain a fungus. {After Bruchmann.) 



single season. Several other species of Lycopodimn, as well as Phylloglos- 

 sum, have a similar type of prothallium but some lack the fungus. 



In most other species, including nearly all those of the North Temperate 

 Zone, the prothallium is larger, commonly 12 to 18 mm. long, and entirely 

 subterranean, colorless, and saprophytic (Figs. 182 and 183). An endo- 

 phytic fungus, restricted to the lower portion of the prothallium, is 

 always present and seems to play an essential part in its nutrition. The 

 spores do not germinate for 3 to 8 years and the prothallium may not 

 reach maturity for an equally long period, growth being extremely slow. 

 The production of sex organs may continue for a number of years. The 

 gametophyte may be erect and somewhat turnip-shaped, as in Lycopo- 

 dium complanatum, with the sex organs borne on an irregularly lobed 

 crown that is not as well developed as in Lycopodium cernuum (Fig. 182). 

 In certain other species, such as Lycopodium davatum, the crown is 

 reduced even more, the prothallium being flat and irregularly cup-shaped, 

 with a depressed center surrounded by a broad rim (Fig. 183). The sex 

 organs are borne in the center. This type of prothallium grows farthest 



