268 INTRODUCTION TO BOTANY 
It may grow about the edge of the water or upon extremely 
wet soil that has been formed by the partial decay of plants. 
On account of the peculiar structure of the leaves these plants 
hold water in great quantities. The leafy shoot of Sphagnum 
continues its growth at the tip from year to year, while the 
older submerged portions gradually become partially decayed 
and intermingled with other plant material. A semi-solid sur- 
face of soil is gradually formed, and this often supports many 
kinds of plants beside Sphagnum. After long periods of accu- 
mulation the partially decayed material becomes compressed by 
the increasing weight above it and is known as peat. When 
removed aud dried (sometimes compressed into bricks), it is 
used as fuel and finds a market in many parts of the world. 
Sphagnon is quite commonly used as a packing material and 
also for holding moisture about potted plants. 
254. General characteristics of the liverworts. These pecul- 
iar plants (fig. 206) take their name from their supposed 
resemblance to the human liver. Most of them grow in moist, 
well-shaded regions, though sometimes they are quite exposed 
and in a few cases they may even grow in intense light and 
heat. Few of them look much like mosses, but some have 
leaf-like structures which quite closely resemble them. 
The most commonly found liverworts lie flat upon the 
ground or upon whatever supports them. From the under- 
surface many rhizoids grow. The plants are usually dark 
green, being abundantly supplied with chlorophyll. They grow 
forward, the lobes continuing to branch until solid mats are 
formed. Older portions of the plant die, leaving the younger 
branches as new and independent plants. 
In some liverworts, cups form on the upper surface, and in 
these cups small, flattish, green buds are developed. These 
buds, when they fall from the cups or are removed in some 
other way, may grow into new liverwort plants. Also, in such 
liverworts as those shown on page 26%, upright stalks grow 
from the prostrate parts of the plants, and in the heads that 
are produced on the ends of these stalks the sex organs are 
