PTERIDOPHYTA. 231 



stem. The leaves are small, simple, sessile, and imbricated, 

 and usually bear a considerable resemblance to those of 

 Mosses. The roots are mostly slender and dichotomously 

 branched. 



429. The Lycopods are for the most part terrestrial per- 

 ennials. They are usually of small size, rarely exceeding 

 a height of 15 or 30 centimetres (6 or 8 inches). 



430. The spores of the Lycopods are produced in spore- 

 cases on the upper side of the leaves. In some of the 

 genera the spores are of one kind ; while in others they are 

 of two kinds, large ones (macrospores) and small ones 

 (microspores). 



431. The sexual plant (prothallium) is but little known 

 in the genera with but one kind of spore; it appears, 

 however, to be a thickish mass of tissue, which develops 

 underground, and bears both kinds of sexual organs. In 

 the genera with two kinds of spores the macrospores pro- 

 duce small cellular growths, which project slightly through 

 the ruptured spore-wall, and upon these several or many 

 archegones are formed; the microspores produce very 

 small, few-celled growths, each of which bears a single 

 antherid, in which there are developed a few anthero- 

 zoids. 



There are about 480 species of Lycopods, distributed 

 among three orders, viz. : 



432. The Club-mosses (Order 33, Ltcopodiace^) are 

 terrestrial plants with many small, generally moss-liko 

 leaves covering the stems. The spore-bearing leaves are 

 often crowded towards the summits of certain branches, in 

 some cases forming well-marked cones (Pig. 138, s). The 

 spores are all of one kind, and are borne in roundish 

 spore-cases, which are generally single on each leaf. 



