CHAPTER XI 

 DIVISION 2. BRYOPHYTA: THE MOSS PLANTS 



THESE are the simplest of the land plants. They include 

 the true Mosses, the low, dense, tufted, ground plants 

 known to everybody, together with the less familiar Liver- 

 worts, which lie close to the ground, and are found in some- 

 what moister places. Over 16,000 species are known, mostly 

 Mosses, but few have* any economic use. 



All Bryophytes are very low-growing, none rising more 

 than a few inches from the ground. The plant body is 

 typically leafy and upright in Mosses, but creeping and 

 thallose in Liverworts. They have no roots, but send into 

 the soil large hairs, called RHIZOIDS, which perform the root 

 functions. Practically all of them synthesize their own 

 food by aid of chlorophyll, one genus alone of Mosses being 

 saprophytic and none parasitic. Their tissues develop from 

 "definite growing cells, as in higher plants, and are differ- 

 entiated into epidermis with stomata, chlorenchyma with 

 intercellular spaces, and elongated conducting cells, though 

 no true ducts or sieve-tubes occur. This lack of a vascular 

 system is without doubt the reason why they do not grow 

 taller, their height being limited presumably by the distance 

 through which water can be raised by diffusion from cell to 

 cell in sufficient abundance for their needs. The intercellular 

 air system, first developed in this group, permits aeration 



- . -I... ,, . ill! 



of deep-lying tissues, and hence more massive growth than 

 is possible in water plants proper (page 562). 



Reproduction occurs partly through diverse vegetative 

 means, and partly through regularly alternating sexual and 

 asexual methods. In the sexual reproduction, an egg cell 

 formed in an elongated flask-shaped ARCHEGONIUM (char- 



478 



