THE HORSETAILS. 57 



ing in length to the apex of the frond. Occasionally, 

 however, the branches at the apex are nearly as long 

 as those below. The branches of each whorl spread 

 out nearly horizontally, and each is again branched, 

 the longest branchlets being nearest the stem. The 

 effect produced is that of a series of circular green plat- 

 forms diminishing in size upward, with the main stem 

 as a central column. The fine and slender branchlets 

 with drooping tips make the whole frond exceedingly 

 delicate and graceful. This is the only species in the 

 world in which the branches are again regularly 

 branched. In some cases the secondary branches are 

 also branched. 



The rootstock of the wood horsetail is slenderer than 

 that of Equisetum arvense; otherwise it much resembles 

 it. The sheaths of the secondary rootstocks, however, 

 are better developed, though the buds from which the 

 fertile spikes are produced are smaller. The secondary 

 rootstocks also bear tubers, though not so abundantly 

 as does Equisetum arvcnsc or Equisetum tclinateia. 

 These tubers are usually much larger than those of 

 Equisetum arvense and are ovate instead of spherical. 



The wood horsetail is found in America from 

 Virginia, Michigan, Iowa, and Nebraska to the Arctic 



WOOD HORSETAIL BUDS AND TUBERS. 



