6 THE FERN ALLIES. 



the same in all, a fusing of the contents of archegonia 

 and antheridia. 



The ferns are a strongly marked and easily recognized 

 group of plants, but the fern allies have no such 

 uniformity of appearance. Only the botanist, familiar 

 with their manner of fruiting, would think of associating 

 plants of such diverse habits and dissimilar forms. The 

 club-mosses usually have trailing vine-like stems and 

 tiny scale-like leaves ; the selaginellas grow in moss-like 

 tufts; the peppervvorts have leaves resembling four- 

 leaved clovers ; the quilhvorts have very short trunks 

 and grass-like leaves ; while the scouring-rushes, at first 

 glance, seem to have no leaves at all and to be chiefly 

 remarkable for their development of stem. Neverthe- 

 less, all are practically alike in their manner of fruiting 

 and in the structure of the plant body, and are therefore 

 properly classed together. 



The great diversity of leaf and stem in the fern allies 

 is made necessary by the habitats of the plants. The 

 club-mosses live on dry moors, in rocky wastes, or 

 sandy swamps; the scouring-rushes in damp shades or 

 standing water. The water-fern is found floating on the 

 surface of- quiet pools ; the marsilias root beneath the 

 water and send their leaves to the surface ; while many 

 of the quilhvorts pass their entire life at the bottom of 

 rivers, lakes, and ponds. 



As a whole, the fern allies are members of a decadent 

 group, and the lack of close resemblances between the 

 families is doubtless to be explained upon the supposi- 

 tion that many of the intergracling forms have died out. 

 At present there are about seven hundred living species, 

 or approximately one for every six species of ferns. In 

 the remote past they were much greater in both num- 



