68 AMERICAN FERN JOURNAL 
the writer’s opinion, to be established as sub-genera. 
None of the important characters, such as apiculate 
cones, evergreen stems, branching systems, distribution 
of stomata, and character of sheaths, give distinct 
ais lace As Clute stated a number of years ago in 
his “‘ Fern Allies,” “‘The manner of growth, the structure 
of the stem, and the method of fruiting are the same in 
all.’ 
Below is given a list of North American species on a 
conservative basis. Varieties, fluctuations and hybrids 
will not be considered in the present paper. Fluctua- 
tions are to be seen everywhere but there are few varie- 
ties so called that are distinct altho many have been 
described. Some forms described as species may be 
good varieties and there are apparently several hybrids. 
The writer is under obligations to William R. Maxon 
of the Smithsonian Institution for assistance in verifying 
certain references given in the list of species. 
SECTIONS OF THE GENUS EQUISETUM. 
I. Cones tipped with a rigid point; aerial stems perennial, with 
re whorls of branches; stomata commonly in bands of 
two or more regular rows each, some with single rows of 
stomata. 
EQUISETA PRIMITIVA. 
Mostly tropical species; none in our region. 
II. Cones tipped with a rigid point; aerial stems perennial, usually 
without whorls of branches except when the main stems are 
broken, but often much branched below the ground, at the 
surface, or rarely from the lower nodes above ground, com- 
monly tufted; stomata commonly in single rows, rarely with 
bands of two or more rows. 
EQUISETA HIBERNA. 
E. laevigatum A. Br., E. praealtum Raf., E. hiemale L., E. 
variegatum Schleich., E. scirpoides Mx. 
III. Cones without a point, rounded or merely acute at the tip; 
aerial stems annual in regions of frost, usually unbranched 
unless broken, but occasionally with whorls of short branches 
on the fertile ones, usually tufted and sometimes also with a 
rosette-like mass of branches about the base of the fertile 
ones; stomata in regular rows, the rows sometimes double. 
QUISETA AMBIGUA. 
E. kansanum Schafin., E. funstoni A. A. Eat. 
