436 



PTERIDOPHYTES (FERN PLANTS) 



Sporophyte. — The stems or shoots that appear above ground 

 are only branches of a creeping, perennial, underground stem. 

 (Fig. 390.) The shoots appearing above ground are of two kinds. 

 One kind, called fertile shoot, bears spores, and the other, called 

 sterile shoot, only makes food. The shoots appearing above ground 

 and the underground stem constitute the sporophyte of Equisetum. 



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

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

 (X i). B, a portion of a sterile or vegetative shoot (X J). C, asporophore, 

 showing the stalk and umbrellas-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). 



The underground stem stores food for the development of new 

 shoots each season and this accounts for the early appearance in 

 the spring of the shoots above ground. The leaves are mere scales 

 so joined as to form a sheath at each node. The sterile shoots 

 branch profusely 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 aerial shoots in the epidermis 



