NortH AMERICAN EQUISETUM 69 
IV. Cones without a point; aerial stems annual, all green, with or 
sometimes without whorls of branches at the nodes; stomata 
in regular lines or bands in the grooves. 
EQUISETA AESTIVALIA 
E. fluviatile L., E. palustre L. 
V. Cones without a point; aerial stems annual, of two kinds, 
sterile ones much branched and green, and fertile ones 
yellowish or brownish in color with little or no chlorophyll 
before the spores are matured and either withering at the tip 
and developing green branches below, or withering completely 
after the spores are shed; stomata scattered in bands or irre- 
gular rows in the grooves or entirely absent on the internodes 
of the fertile shoots. 
UISETA HETEROPHYADICA. 
E. silvaticum L., E. pratense seals E, telmateia Ehrh., £. 
arvense 
PHYLETIC Synopsis OF EQuIsETUM, ee Awad 
pEcIES NortH oF MEX 
I. Cones tipped with a rigid point, the termination of the floral axis; 
aerial stems evergreen. 
A. Sheath segments and deciduous teeth sharply differentiated; 
aerial stems usually tall and rigid, ees many-grooved (10- 
+); — cavity of the internode larg 
1.8 gated, dilated ental so as appear more or less 
funnel-shaped, green in age, with a black or brown limb, 
sometimes witha Aock band sien sheath segments slightly 
tricarinate; stems rather smoothish. E. laevigatum 
2. Sheaths short, cylindrical, appressed, ash-colored or black | in 
age, often with a black ring around the limb and a second 
one at the base, not dilated above patil when young, but 
frequently split in age; stems very r 
a. Ridges of the stem with one row of shade sheath seg- 
i e 
minute 
b. Ridges of the stem with two rows of tubercles; sheath seg- 
ments with a deep central groove, normally quadricarinate. 
E. hiemale. 
B. Sheath segments and teeth not sharply differentiated, the base 
of the teeth usually persistent, but the bristle tips deciduous; 
stems low and slender, tufted, usually 10-grooved or less, solid 
