EQUISETUM. 
269 
usual size, and sometimes reduced in 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 alpinum. 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. mriegatxm^ but is distinguishable by means 
of its sheaths and fructification. 
The variety, or form, called polystacJiyoUj is probably 
rather accidental than constant, and is to be regarded as 
the result of peculiar and changeable circumstances which 
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 
