THE VASCULAR CRYPTOGAMS 81 



roots, which arise at the nodes, and in this species also 

 produces round tubers, each of which represents a short 

 branch consisting of a single swollen internode. These 

 tubers are capable of giving rise to new plants, and thus 

 form a means of vegetative propagation (see Fig. 38, 2, a). 



The characters of the stem are best studied in detail 

 on the shoots which rise above the ground. The surface 

 is ribbed lengthwise, each rib lying in the same straight 

 line as one of the leaves of the node next above. Both 

 ribs and leaves alternate regularly in successive inter- 

 nodes. The stems above ground are in this species 

 (E. arvense) of two kinds. First, we have the fertile 

 shoots, which show themselves in spring (March) and 

 have no other function than to bear the cones (Fig. 38, 

 1). These fertile shoots are unbranched, and are of a 

 pale colour, containing little or no chlorophyll. They die 

 down as soon as the spores are shed. The other shoots 

 are sterile, and their branches constitute the assimilating 

 apparatus of the plant, for the leaves are of little im- 

 portance in this respect (Fig. 38, 2.) They are of a deep 

 green colour, and are repeatedly branched, the branches 

 breaking out from the stem through the lower part of 

 the leaf-sheaths. In each whorl the branches are equal 

 in number to the leaves, and alternate with them. The 

 ultimate ramifications are very slender, and only have from 

 three to five ribs, while the main stem may have as 

 many as twenty. The surface of the aerial shoots is 

 very hard and somewhat rough, especially at the ridges. 



We see then that our plant has a very characteristic 

 habit, marked partly by the small development of 

 the leaves, and partly by the great regularity of the 

 whorled branches. Other species differ considerably from 

 this type ; many have only one kind of stem, the cones 

 6 



