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. , Economic 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 

 oosphere, 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. Relation of 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 flowfering 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 oosphere, and that 

 part of the contents of the pollen-grain corresponds to the 

 antherozoid." 



' Pteris aguilina. 



' See Strasburger, Noll, Sohenk, and SoWmper, Lehrbuch, pp. 364-367, and Potter's 

 Warming's Syatematio Botany, pp. 234-250. 



