HORSETAILS 



423 



curs at each joint. (See Figure 215.) Equisetums grow, in 

 both dry and wet places. They are often found on rail- 

 road embankments. 



Reproduction. — 

 Equisetums have un- 

 derground stems as 

 well as aerial stems 

 and their underground 

 stems live over winter. 

 One of the commonest 

 kinds produces uu- 

 branched shoots 

 the spring before 

 branched shoots 

 pear. These 



m 



the 



ap- 



un- 



branched shoots bear a 

 yellowish, cone-shaped 

 structure at the top. 

 (See Figure 215.) This 

 structure is composed 

 of peculiar leaves, each 

 of which is shaped like 

 the letter T. Only the 

 tops of the T's are vis- 

 ible. The bottoms are 

 attached to the stem. 

 The tops fit closely to- 

 gether, forming the 

 surface of the cone. 

 On their under sides 

 these leaves bear spo- 



FiG. 216. — Bolrychium. The moonwort. One 

 of the true ferns which does not bear its 

 sporangia on the under side of the green 

 leaves, but upon specialized parts. In this 

 fern the uppermost part of the frond is de- 

 voted to spore production. It is a case of 

 partial differentiation of a sporophyll. 



