CORN-FIELD EQUlSETUM. 
81 
never seen the teeth of this species with the distinct white semi- 
hyaline membrane, which appears constant in E. palustre, E. 
umbrosum, and some other species. There is a whorl of branches 
on each of the thirteen upper joints, the eight lower ones being 
branchless : the number of branches in a whorl varies from four 
to thirteen. The branches are eight to ten inches in length, ra- 
ther stout, spreading, slightly ascending, four-ribbed and com- 
posed of ten or twelve joints, of which the apical ones are 
shortest ; the basal joint is shorter than the three which follow 
it, but it is much longer than in E. palustre, and still more so 
than in E. umbrosum : the short sheath at the base of each 
branch usually terminates in obtuse brown segments : the other 
sheaths are loose, and terminate in four long acute teeth, which 
are generally concolorous throughout, and a single rib invariably 
ascends undivided to the extreme point of each. 
The more strongly marked variations of the barren stem are 
these. — 
A. — Stem erect ; branches simple, very rigid, erect, and 
densely crowded. 
B. — Stem erect ; branches simple, less rigid, spreading, 
slightly ascending. 
C. — Stem erect; branches simple, gracefully drooping. 
D. — Stem erect ; branches compound, in the same manner as 
in E. sylvaticum, and gracefully pendulous. 
E. — Stem almost prostrate, with semi-erect, very long, com- 
pound feeble branches. 
F. — Stem prostrate, with scattered, simple, irregular, semi- 
prostrate branches. 
The right hand diagram represents a section of the stem of 
Eo umbrosum^ the left hand of E. arvense. 
G 
