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A TEXT-BOOK OF BOTANY. 



as quillworts. The plants produce a number of filiform roots 

 which penetrate the mud, and a compact tuft of rush-like leaves. 

 The plants are heterosporous, as in Selaginella. The sporangia 



Fig. 6o. Selaginella helvetica. A, sporophyte consisting of leafy branches giving 

 rise to microsporangia (i), megasporangia (g), and rhizoids (r) ; B, longitudinal section of 

 portion of branch showing a megasporangium (g) with 3 megaspores in view, a microspor- 

 angium (i) containing microspores; C, a young microsporangium showing free mother cells 

 before formation of tetrads; D, tetrahedral division of spore mother cell; E, ripe megaspore; 

 F, four microspores of tetrad separated; G, microsporophyll seen from above showing ripe 

 microsporangium. — After Dodel-Port. 



are borne in the axils of the leaves, the outer leaves bearing the 

 megasporangia and the inner leaves the microsporangia. The 

 gametophytes consist of but a few cells. While the group is het- 



