EQUISETUM. 269 



usual size, and sometimes reduced ia size like the lateral 

 heads. The lateral heads are usually later in their appear- 

 ance than the central ones. Occasionally we have seen 

 some of the branches of the lowest whorl become elon- 

 gated, and terminate in one of these small cones. 



Another form is called nudum, and a very similar variety 

 is sometimes called alpinuni. There appears to be no 

 advantage in attempting to distinguish these, both being 

 depauperated forms, depending no doubt on the circum- 

 stances of their growth. They differ from the ordinary 

 plant in being altogether smaller, the height ranging from 

 two to four or five inches, the lower part of the stems 

 being decumbent, and the whole stem almost devoid of 

 branches ; a few being developed only at their very base. 

 In some states, this form has much resemblance to the 

 prostrate E. tariegatum, but is distinguishable by means 

 of its sheaths and fructification. 



Tlie variety, or form, called poli/stachyon, is probably 

 rather accidental than constant, and is to be regarded as 

 the result of peculiar and changeable circumstances wliich 

 may influence its growth. The variety nudum, or alpinum, 

 seems clearly a depauperization of the plant, either through 

 elevation or lack of food, both producing the result of a 



