(3o) 



or saprophytic in their mode of life; the lichens form an inde- 

 pendent symbiotic group, each lichen consisting of a fungus 

 and an alga living together, the one nourishing the other. 

 The lichens are quite familiar to most people as plants of 

 more or less leathery texture growing on rocks, on poor soil 

 or on the trunks of trees. 



A step forward brings up to the Bryophyta, or seedless 

 plants with roots, stems and leaves, but without vascular tis- 

 sue (cases 37 to 48) . This group is best known through the 

 mosses, which form its largest division ; but of simpler struc- 

 ture are the hepatics or scale-mosses (cases 37 to 40) ; al- 

 though they were formerly associated with the true mosses, 

 their tissues are much less differentiated than those of the 

 mosses and the structure of their various organs much less 

 complicated. The stems and leaves of the hepatic plant 

 are sometimes combined into a flat thallus-like body which 

 creeps closely on the ground or other objects and resembles 

 in aspect some of the more simply organized plants. The 

 leaves, too, are more like scales than in the true mosses and 

 they do not have a midvein. These differences alone enable 

 one to distinguish a hepatic from its relatives by the unaided 

 eye or at most by the use of a lens. In addition to these 

 characters, the capsule or the receptacle which bears the 

 spores, or reproductive bodies, usually splits into four valves 

 when full-grown and the spores themselves are accompanied 

 by spiral threads called elaters. The favorite habitat of 

 hepatics is wet places, and mountains continually steeped in 

 clouds yield a surprising variety of forms. Closely related 

 to the hepatics is the group Anthocerotes; these plants may, 

 however, be distinguished by the presence of a central axis or 

 column (columella) in the capsule, and there are several 

 other important structural differences in their tissues. 



The mosses (cases 41 to 48) follow the hepatics in order of 

 development and complexity; they differ from them, however, 

 in many respects. The stem and leaves have more differen- 

 tiated tissues, and the leaves usually have a midvein. The 

 moss capsule generally opens by a lid under which there are 



