332 



SPORES OF SELAGINELLA 



mass. When moistened, the absorption of water causes the 

 branches to quickly uncoil and also renders the tissues translu- 

 cent, so that the green color of the chloroplasts can be seen. 

 These reactions occur even in the dead plants and so create the 

 impression that they have returned to life. Many of the species 

 of SelagineUa have a creeping habit like that of Lycopodium, 

 and the aerial stems are covered with leaves arranged in several 

 rows, very frequently in four rows of two large and two smaller 



Fig. 242. Sporophylls and spores of SelagineUa: 2, strobilus with lower 

 sporophylls separated for spore dissemination. 3, megasporophyll with 

 sporangium containing four megaspores. 4, microsporophyll. 5, mega- 

 spore enlarged. 6, microspore equally magnified. 6A, more enlarged view 

 of the microspore. The triangular surfaces of the spores show that these 

 spores have been formed in tetrads from a spore mother cell as in previous 

 groups. 



leaves (Fig. 241, i^l). Usually but a single chloroplast appears 

 in each cell, as already noticed in several algae and in the Antho- 

 cerotales. The roots are frequently developed from the end of 

 naked branches that extend from the stems to the ground (Fig. 

 241, r). 



(a) Sporangia and Spores. — The sporangia are borne on the 

 stems in the axils of the leaves which form a strobilus, as in 

 Lycopodium. However, they differ radically from those of the 

 Lycopodium, in that two kinds of spores are formed, small spores 



