98 



PLANTS AND MAN 



ground cedar form sinuous growths close to the earth; and the 

 numerous club-mosses grow stiffly erect with shining dark green 

 leaves. Some of the species are used as Christmas greens. 



A third group is the Horse-tails (fig. 69) with less than 50 

 species. One of their characteristics is a segmented stem lacking 

 leaves; these photosynthetic organs have become reduced to 

 whorls of small scales while the stems are green and carry on 



Fig. 68. — Creeping pine is a fern relative with minute scale-like leaves. 



photosynthesis. The horse-tails are usually swamp-dwelling 

 plants rarely more than a few feet in height. Scouring-rushes have 

 cylindrical stems which lack the whorls of lateral branches 

 characteristic of the horse-tails. This entire group, as well as that 

 of the club-mosses, differs from the true ferns in having the spores 

 produced in terminal cone-like structures. 



Pteridophytes today are of little economic importance, except 

 as ornamental plants. In the geologic past, however, their 



