SOME TYPES OF FLOWERLESS PLANTS. 245 
the bracken-fern, or brake,’ and in Osmunda, very large in , 
proportion to the parts of the plant visible above ground. 
304. Hconomic Value of Ferns. — Ferns of living species 
have little economical value, but are of great interest, even 
to non-botanical people, from the beauty of their foliage. 
During that vast portion of early time known to geologists 
as the Carboniferous Age the earth’s surface in many parts 
must have been clothed with a growth of ferns more dense 
than is now anywhere found. These ferns, with other flower- 
less herbs and tree-like plants, produced the vegetable matter 
out of which all the principal coal-beds of the earth have 
been formed. 
305. Reproduction in Ferns. — The reproduction of ferns 
is a more interesting illustration of alternation of generations 
than is afforded by mosses. The fruiting plant is the minute 
prothallium, and the non-fruiting plant, which we commonly 
call the fern, is merely an outgrowth from the fertilized 
odsphere, and physiologically no more important than the 
urn of a moss, except that it supplies its own food instead of 
living parasitically. Like this urn, the fern is an organism 
for the production of unfertilized spores, from which new 
plants endowed with reproductive apparatus may grow. 
306. Lelation ¢f Reproduction in Ferns to that in Flowering 
Plants. — Botanists have been able to trace out in great detail 
the true relation which such forms of reproduction as occur 
in mosses and in ferns bear to that of flowering plants. 
Stated in the merest outline their conclusions are that the 
nucleated ovule cell or egg-cell (e, Fig. 142) which is fertilized 
by the pollen tube corresponds to the odsphere, and that 
part of the contents of the pollen-grain corresponds to the 
antherozoid.? 
1 Pteris aquilina. 
2See Strasburger, Noll, Schenk, and Schimper, Lehrbuch, pp. 364-367, and Potter’s 
Warming’s Systematic Botany, pp. 234-250. 
