INTRODUCTION 3 



orders are dependent upon roots for absorbing most of 

 their food and moisture and this is carried up through 

 the stem and distributed to all parts of the plant by 

 means of conducting cells. The leaves, as well as other 

 parts of the plant, are entirely surrounded with a 

 special layer of cells the outer walls of which contain a 

 substance called ^'cutin," which renders this coating 

 practically water- and gas-proof. This waterproof 

 coating prevents excessive evaporation and also ab- 

 sorption of water. Mosses, on the other hand, are not 

 dependent upon roots for absorbing water, and the 

 leaves and other parts of the plant are not provided 

 with a waterproof coating. This structure not only 

 causes mosses to dry easily, but also enables them to 

 absorb water quickly through the entire surface of the 

 leaves and all parts of the plant and so resume the 

 appearance of fresh plants when dried specimens are 

 placed in water. 



Mosses are widely distributed, and are found in all 

 sorts of places except in salt water. They grow on 

 moist and on dry ground ; on bare rocks and ledges and 

 on those that are covered with soil; on trees; on decay- 

 ing wood, such as old logs and stumps; on old roofs; 

 and even in streams and ponds and in places that are 

 sometimes submerged. They are especially abundant 

 in cool, moist woods and luxuriant swamps where old 

 logs are rotting, but many may be found in drier and 

 more open places, such as old fields and meadows, 

 and even along the roadside. 



