'HE SCOURING-RUSHES. 



39 



The greatest number of mature spikes \\ ill probably be 

 found about the middle of April, making it one of the 

 earliest fruiting species of Equisctiuu. 



The stems grow in dense tufts, the longest barely 

 reaching a height of ten inches, and are so slender as to 

 be almost threadlike. They are often branched 

 at base, but seldom so above, unless they become 

 prostrate and covered with soil. The feitile stems 

 are nearlj^ erect, but the sterile are flexuous and 

 bend over at the tip. When dried for the herba- i\iB[/yi 

 rium they often coil into circles or even double 

 circles. The stem is six-angled, but there are 

 only three leaves in the sheath. In all other 

 species of Equisetum the number of leaves in the 

 sheath and the number of angles in the stem are 

 equal, and the apparent anomaly presented by 

 this species is explained by the fact that in addi- 

 tion to the true ridges there is an equal number 

 of false ridges over the vallecular canals. The^"^'^^"' 

 three leaves are not joined together, and do not prop- 

 erly form a sheath, in this showing very clearly that the 

 sheaths of the other species are formed of confluent 

 leaves. The teeth are small, slender, black, with pale 

 margins, and are not deciduous. The leaves have one 

 deep central groove and two lighter lateral ones, making 

 them four-keeled. In age, both leaves and sheaths be- 

 come dark brown or black. Unlike all other equisetums, 

 the stems of this species have no central hollow. The 

 vallecular canals are comparatively large, and the carinal, 

 though small, are present. 



The fruiting-spikes are scarcely larger than pepper- 

 corns and consist of about half a dozen small sporophylls 

 on an axis tipped with a tin}' black point. JNIan^' of the 



