THE SCOURING-RUSHES. 



its diameter, and the contained air causes a loud 

 report when it is forced out under pressure. 



The great scouring-rush is rare east of the Mis- 

 sissippi River except in the South. It has been 

 reported, apparently upon good authority, from 

 scattered stations in New Jersey, Pennsylvania, 

 Maryland, Indiana, Illinois, and Michigan, and is 

 the common form in the States bordering the Gulf. 

 In the West it appears to be plentiful throughout, 

 extending northward into British Columbia. It 

 is said to occur in India also. The stems are as 

 rough as those of the common species, and are still 

 occasionally used for polishing by the Southern 

 negroes. Being so nearly \ikt Eq7iis£ii/7n hiemale \X. 

 shares with it the various common names. 



T'he Slender Scouring-Rush. 



The characters relied upon. for the identification 

 of the various Equisetziin species, such as the num- 

 ber of grooves in the stem, the diameter of the 

 stem, length of the joints, etc., make the variations 

 a matter of easy mathematical demonstration. In 

 I making some investigations along this line, recently, 

 the author was surprised to find that the extremes 

 of variation in Equisetiim hiemale are mucli less 

 than is commonly supposed. Out of more than 

 250 stems selected at random, all but twenty-four 

 were between 5/32 and 8/32 of an inch in diam- 

 eter. The length between joints was between 

 two and three inches in all but fifteen of the 

 Equisetum 2^o spccimens measured, while of 12=1 speci- 



Ferrissi. J 1 J r 



Section of mens in which the grooves were counted, all 



Stem, ^ 



Natural but thirteen had from twenty-four to thirty 



Size. ^ '^ 



