EQUISETUM. 237 



some curious variations to which this plant is liable. One 

 of the most remarkable has been called the variety poly- 

 stackion. It is remarkable in having more or less of the 

 branches of the two upper whorls terminating in cones of 

 fructification; the usual habit of the plant being to pro- 

 duce only one cone, and that on the central stem. The 

 cones produced by the branches are, we believe, always 

 much smaller than the ordinary cone of fructification pro- 

 duced by the main stem, and they are darker-coloured and 

 more compact. It has been suggested, that the production 

 of these lateral fructifications is accidental, owing to the 

 destruction of the top of the main stem, but this explana- 

 tion is quite insufficient, since they are sometimes produced 

 along with the central head, which moreover varies when 

 accompanied by them, being sometimes of the usual size, 

 and sometimes reduced in size like the lateral heads. The 

 lateral heads are usually later in their appearance than the 

 central ones. Occasionally we have seen some of the 

 branches of the lowest whorl become elongated, and termi- 

 nate 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 ad- 

 vantage in attempting to distinguish these, both being de- 



