DEVELOPMENT OF PLANTS 327 



true of the male gamete, which is small and not spirally coiled 

 and it is apparently biciliate (Fig. 240). 



The lycopodiales are largely tropical, though a small number 

 of forms are of common occurrence in temperate regions. The 

 stems are erect or creeping and rather small, but owing to their 

 prolonged growth and extensive branching they often form con- 

 spicuous and attractive colonies. The tissues of the stem do 

 not materially differ from those of the common fern, though the 



Fig. 237. Cross-section of a portion of the stem of Lycopodiunt, showing 

 the centrally arranged vascular bundles. 



vascular bundles are centrally placed and often appear as radiat- 

 ing plates (Fig. 237). The work performed by the leaves, as 

 in the Equisetales, is usually of two kinds, namely, photosynthe- 

 sis by the green foliage leaves and spore production by the leaves 

 that usually form strobili at the tips of certain branches. But a 

 single sporangium is associated with each of these sporophylls 

 (Fig. 239). 



The club mosses are a very much larger group than the Equise- 

 tales, but like the latter group, they are a remnant of a highly 

 developed and widely distributed race. Fossil remains indicate 



