MOSSES, LIVERWORTS, AND FERNS 267 
252. The nutrition of mosses. The stem-and-leaf arrange- 
ment of the mosses exposes chlorophyll to the light in a differ- 
ent way from that which was found in the alge. With the 
leaves arranged radially about the stem 
much more chlorophyll is exposed than 
could be exposed in the same space by 
a prostrate plant. The importance of 
the stem in holding these leaves up 
into the air, thus making the radial 
arrangement possible, is great. The 
expanded portions of the leaves are a 
single layer of cells in thickness, while 
the median portion may consist of 
several layers. Moss plants are often 
favorably placed for securing mois- 
ture when moisture is abundant. The 
whole dense growth made by the 
hundreds of plants that grow together 
may act as a sponge in absorbing and 
holding water, so that at times, when 
one is walking through mosses, water 
runs in streams from those upon 
which he steps. Certain mosses live 
part or all of the time directly in the 
water. On the other hand, when long 
exposed to drying influences, some 
mosses become so dry that they readily 
crumble; but if not disturbed, they 
proceed to grow whenever there is a 
return of adequate moisture. Moses 
may also withstand great extremes 
of heat and cold. 
253. Peat-bog moss. There are many different kinds of 
mosses, and they are found in almost all kinds of places where 
any plants grow. Peat-bog moss (Sphagnum) (fig. 205) is a 
very striking form which, with other plants, often forms peat. 
Fie. 205. A peat-bog moss 
(Sphagnum) 
About natural size 
