THE FORMATION OF COAL AND PEAT 339 
branches in a circle around each 
joint. The conductive tissue in 
this plant is arranged near the 
center of the stem (Figure 315). 
Selaginella is seldom seen in 
northern latitudes, except in 
greenhouses. 
288. Economic Importance. — 
The fern group, like the mosses, 
have little economic importance. 
The spores of the club mosses are 
used in making certain kinds of 
fireworks (especially those used 
indoors); also in drug stores to 
keep pills from sticking together. 
The plant itself is used in Christ¬ 
mas decoration. Horsetail, so named from its appearance, 
is a common plant in waste places. Another plant in this 
group was formerly cut, tied in bundles large enough to be 
held easily, and used for scouring woodwork or tinware, 
which accounts for its other name, 
the “ scouring rush.” 
289. The Formation of Coal and 
Peat. — Ages ago ferns were more 
numerous than they are now and 
many of them grew to be as large as 
our present trees. Geologists tell us 
that the climate was warmer and 
more moist than it is now, and condi¬ 
tions especially favored the growth 
of fern plants. Where these large 
ferns died and fell to the ground, great masses accumulated. 
As the earth’s surface changed, these masses became 
covered with soil or water, and under the influence of heat 
and pressure they, together with other plants (gymnosperms), 
A , spore equisetum ; 
B, elators. 
Figure 313. — Sporophyll (en¬ 
larged). 
A, sporophyll; B, sporangium; 
C, spores; D, spores (enlarged). 
