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PLANT MORPHOLOGY 



simplest species of Lycopodium all the leaves are sporophylls, but in the 

 more advanced species a differentiation exists between sporophylls and 

 foliage leaves, the former forming a more or less distinct strobilus. All 

 the Lycopodiales are homosporous. Dehiscence of the sporangium occurs 

 by means of a transverse slit. The gametophyte is a subterranean tuber- 

 ous body, sometimes with an aerial portion. The antheridia develop 



Fig. 186. Development of the embryo of Lycopoduim clavatum. A, first division of the 

 fertilized egg into suspensor and embryonal cells; B, second division of embryonal cell; C, 

 second division of suspensor cell; D, cross section, showing third division of embryonal cell; 

 E, transverse division (IV) of four cells derived from the embryonal cell; F, G, H, later 

 stages; /, young sporophyte, showing foot (/), primary root (r), and stem bearing scale 

 leaves. {After Bruchmann.) 



endogenously and produce many small biciliate sperms similar to those 

 of bryophytes. The archegonia are primitive, being characterized by a 

 large number of neck canal cells. The embryo has a suspensor. On the 

 whole, the Lycopodiales are a very primitive group of pteridophytes. 



2. Selaginellales 



The Selaginellales include a single genus, Selaginella, mth nearly 700 

 species. The great maj ority of these are tropical or subtropical in distri- 

 bution, but a few occur in temperate regions. Most species require 

 abundant moisture and shade, while some grow in open, dry situations. 

 Selaginellites, a fossil genus, has been recognized in deposits as old as 

 the Lower Carboniferous. 



