202 



Introduction to Botany. 



In order to understand the morphology of the parts of a 

 flower we must refer back to simpler and older types of 

 vegetation. The Lycopodiums or club mosses are repre- 

 sentatives of an ancient group of plants which reached its 



maximum development in the 

 Carboniferous period. There 

 are good reasons for the belief 

 that the Lycopodiums and the 

 flowering plants are offshoots 

 from a common ancestral 

 stock, the Lycopodiums be- 

 ing, of the two, much less 

 modified and more primitive 

 in character. We find in them 

 that the stem is thickly beset 

 with small, awl-shaped leaves 

 (Fig. 120). Near the apex of 

 the stem some of the leaves 

 bear spore cases or sporangia 

 at their bases. In certain 

 species the spore-bearing 

 leaves or sporophylls are 

 broader and longer-pointed 

 than the foliage leaves, but 

 there may be all degrees of gradation between the two 

 forms. In other species there may be no difference in 

 appearance between the foliage leaves and sporophylls. 

 In some species the sporophylls are aggregated into a 

 cone, in others not. 



In the Lycopodiums the sporangia and spores are of one 

 kind only ; but in the somewhat nearly related genus 

 Selaginella, there are two sorts of sporangia, borne each on 

 the stem in the axil of the sporophyll, which in general 



Fig. 120. 



, Lycopodlum clavatum, the leaves ag- 

 gregated into cones at the apices of 

 the branches ; 2, a leaf from the cone, 

 with a sporangium in its axil ; 3 and 

 4, spores from the sporangium. After 

 WOSSIDLO. 



