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TEXTBOOK OF BOTANY 



floating, hairy, entire leaves; the third leaf looks much like a branched 

 root. Stems and roots are more conspicuous in Azolla. The other two 

 genera are larger plants with prominent leaves from rhizomes rooted in 

 the mud below the water. Superficially the leaves of Marsilia resemble 

 a four-leaved clover; those of Pilularia resemble leaves of grasses. 



Two kinds of spores develop in the water ferns: microspores and 

 megaspores. Male gametophytes develop from the microspores, and 

 female gametophytes from the megaspores. Plants that bear both micro- 

 spores and megaspores are said to be heterosporotis ( different spores ) , 

 in contrast to homosporoiis plants in which the spores are all alike and 

 the gametophytes that develop from them are bisexual. 



The Lycopods or Club Mosses 



The club mosses are relatively small in size, frequently evergreen, 

 and flourish especiallv in the tropics. The common name refers to their 



Fig. 313. One of the common club mosses {Lycopodium complanatiim) . The 

 plant pictured here is the sporophyte phase. The sporangia are borne in the terminal 

 cones. Photo by E. S. Thomas, Ohio State Museum. 



moss-like leaves and club-shaped cones. The upright appearance of 

 some species is that of a small pine tree; hence the name "ground pine. 

 Species of the two genera, Lycopodium (Fig. 313) and Selaginella 



