THE PTERIDOPHYTA : LYCOPSlDA, ETC. 619 



possessing a stiff, upright, jointed stem which bears whorls of poorly 

 developed leaves, each whorl being united to form a sheath around the stem 

 at each node. Sometimes the stem produces branches, and in such cases 

 the branches themselves are developed in whorls, further intensifying the 

 formal and geometrical appearance of the plant. 



The cones are borne either at the apex of the main stem or of branches. 

 In some species they develop at the apices of the ordinary vegetative stems, 

 whilst in other species special, fertile, unbranched stems are produced 



Fig. 629. — Eqidsetum arveme. Two assimilating shoots 

 and one fertile shoot with strobilus. Much 

 reduced. 



which are devoid of chlorophyll. These are produced in the early part of the 

 year and are followed later by the green stems. 



These vertical stems are connected underground to a branched rhizome 

 which often penetrates into the ground to a considerable depth. In appear- 

 ance this rhizome is somewhat similar to that of the vegetative stem except 

 that large numbers of adventitious roots are formed at the nodes, arising 

 usually from the bases of the lateral buds. Some branches of the rhizome 

 remain short and develop into tubers, which will grow if detached and serve 

 as a means of vegetative propagation. 



The largest British species, Equisetiim telmateia, may reach a height of 

 some 6 to 8 ft., but most of the other species are smaller, rarely attaining a 

 height of more than 2 ft. 



