422 BRYOPHYTES (MOSS PLANTS) 
In the sporangium there is a columella or axis of sterile tissue, 
and in the sporangial wall air spaces and filaments of green 
tissue are provided. In some Mosses the base of the capsule, 
called apophysis, is devoted to food-making rather than to 
the formation of spores, in which case there is much chlorophyll 
tissue and many stomata present. This feature is quite impor- 
tant as was pointed out in Anthoceros, because it looks forward 
to the independence of the sporophyte; for, if the sporophyte 
can make carbohydrates for itself, it then needs only roots to 
absorb water and mineral salts, in order to live independently of 
the gametophyte. 
The gametophytes of the Mosses have a remarkable power of 
propagating vegetatively. Since the sperms depend upon water 
for transportation and the sex organs are borne above the moist 
substratum, fertilization rarely occurs in some Mosses, which, 
therefore, must depend largely upon vegetative propagation. 
There are a number of ways by which they propagate vegeta- 
tively. First, by the isolation of branches through the death of 
the older axes; second, the cells of the protonema sometimes 
separate, become restive, and later from each resting cell a new 
protonema is developed; third, from the leaves and stems of the 
gametophore new protonemas are often developed; and fourth, 
some Mosses develop gemmae which are commonly borne at the 
summit of the leafy gametophore. 
The Sphagnums (Sphagnales). — The genus Sphagnum in- 
cludes all of the Mosses of this order. There are about 250 
species, and they occur mostly in temperate and arctic regions. 
They live chiefly in bogs and are commonly called Bog or Peat 
Mosses. Their slender, branched, leafy gametophores (Fig. 377) 
are pale in color due to the fact that many of the leaf cells as well 
as many of the outer cells of the stem are empty except for the 
water and air which they hold, thus containing no chloroplasts. 
It is due to the ability of these much enlarged empty cells to 
take up and retain water by capillarity that Sphagnum retains 
moisture so well when used in germinating boxes or for moist 
packing around plants. The gametophores are commonly 
creeping, turning up only at the ends, and they usually form close 
mats, which gradually thicken by growth above and eventually 
fill up bogs. Due to the indefinite growth at the tips, gameto- 
phores may attain great length and age. In bogs where, due to 
