436 



PTERIDOPHYTES (FERN PLANTS) 



Sporophyte. — The sporophyte consists of a horizontal, much 

 branched, underground stem from which two kinds of aerial 

 branches or shoots arise {Fig. 390). One kind of shoot bears 

 spores and is called a fertile shoot, while the other kind does only 

 vegetative work and is called a sterile shoot. Both kinds of 



Fig. 390. — Equisetum arvense. A, a portion of the underground stem 

 with two fertile or spore-bearing shoots, each of which bears a strobilus (d) 

 (X h)- B, a portion of a sterile or vegetative shoot (X j). C, asporophore, 

 showing the stalk and umbrella-like top on the under surface of which are the 

 sporangia (e) (X 6). Below, at the right, are shown spores, one with elaters 

 coiled about the spore and the other with elaters uncoiled (X about 15). 



shoots are formed under the ground in the fall in most Equise- 

 tums and are thus ready to elongate and appear above ground 

 early in the spring. On both kinds of shoots the leaves are mere 

 scales, which are so joined as to form a sheath at each node. The 

 sterile shoots produce whorls of slender branches at the nodes and 

 are so finely branched as to resemble a horse's tail — whence the 

 name Horsetails. The food is made by the green cortex of the 



