52 THE HORSETAILS. 



what, as in the field horsetail. There are sometimes 

 more than twenty whorls of these branches, and from 

 twenty to forty branches in a whorl. Near the tip the 

 whorls are rather close together ; below, they are farther 

 apart, and the lower third of the stem is naked. The 

 average length of the branches is nearly six inches, but 

 in some instances they are three times as long. The 

 sterile stems are pure white, and the sheaths which 

 closely invest them are pale green, with brown teeth. 

 The common name of this species was given in allusion 

 to the colour of these stems. 



Although the ivory horsetail grows in regions where 

 the earth is not penetrated very deeply by the frost, in 

 the North, at least, its stems are strictly annual. The 

 rootstock is similar to that of Equisctuin arvcnse, though 

 larger, and at the nodes it also bears numerous tubers 

 which are as large as marbles. These tubers often occur 

 in necklace-like strings, and show very plainly that they 

 are the swollen internodes of the rhizome. 



Like Equisctuin arvense, this species has numerous vari- 

 eties, mostly of an ecological nature. Late in the year 

 one may find fruiting-cones on the ordinary green stems. 

 In the case of similar cones on the normally sterile 

 fronds of Equisctuui arvense, it has been assumed that 

 they have been caused by an injury to the fertile stems; 

 but in Francis's " British Ferns " it is stated that the 

 cones on Equisctuin teluiateia are caused by drought, and 

 that with specimens grown in pots these cones may be 

 produced at will by withholding water at the proper 

 time. 



Equisetum teluiateia is well distributed in the Old 

 World, being found from Ireland and Scotland to 

 Siberia, Persia, and North Africa. In America it is 



