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30 FERNS OF NORTH AMERICA.
and irregular, mostly simple, spreading roots, both containing-
starch in abundance. Commonly but a single frond is produced
each year. This frond, in all the species, consists of a common
stalk, a posterior sterile segment, and an anterior fertile segment.
The base of the stalk is enlarged, and encloses in a rudimentary
condition the fronds for the next year or two. In the
position of these rudiments, and in their development, a law of
alternation has been observed ; that is, the sterile segment for
one year occupies the position held by the fertile segment of the
preceding year, so that a longitudinal section of the bud contained
in the base of the stalk will show the rudiments for two or even
three years packed closely away, and with the fertile and sterile
segments placed below each other alternately to right and to left.
In B . Virginianum, the very base of the stalk is split open on
one side, more or less disclosing the bud; but in all the other
species there is no such deft, and the bud is completely enclosed.
There is generally also present a loose outer, sheath-like covering,
which is the withered base of the stalk of the preceding year.
Botrychium Lunaria varies in total height from an inch and
a half to a foot; but the greater part of specimens examined
measure from six to nine inches long. Of this length, about a
half—-sometimes a little more or a little less than a half — is
taken up by the common stalk, which is erect, smooth, terete, and
fleshy. The sterile segment is almost always closely sessile, and
commonly from a fourth to a third part of the whole length of the
plant, or from one and a half to three inches long. It is oblong
and obtuse in outline, fleshy, and divided into from two to nine
FERNS OF NOR'J'H AMICRICA. $1
(usually four to seven) pairs of nearly opposite divisions, besides a
smaller (usually two- or three- lobed) terminal division. These
divisions have a broad wedge-shaped base, but rapidly widen out
on both the upper and lower sides, and have the outer margin
rounded, so that they are more or less clearly moon-shaped :
whence the common name of the plant. The outer margin is
either entire, crenulate, or incised ; sometimes deeply so, as in
var. incisitm of Milde. In var. tripartitum (Moore, Nat. Print.
Brit. Ferns, 8° ed., p. 324) the two lowest divisions are elongated
and pinnately parted, rendering the whole sterile segment tcrnate.
The venation is essentially flabellately dichotomous. A single
vascular bundle proceeds from the midrib of the sterile segment
to each division: this vascular bundle or vein forks once at the
very base of the division, and its two branches again where the
division begins to widen, and these veinlets again three or four
times before the outer margin is reached. The fertile segment is
long-peduncled, and usually overtops the sterile segment considerably.
It is twice or thrice pinnately compound, forming a panicle
not unlike a miniature cluster of grapes ; and from this resemblance
the genus takes its name of Botrychium, or Grape-fern.
The spore-cases are globular, about half a line in diameter, and
open transversely into two equal valves. Their texture is sub-
coriaceous., and no vestige of a ring can be observed. The spore-
cases of all the species of the genus are essentially alike in all
respects. The spores are pale or colorless, roundish-tetrahedral,
having the general surface minutely roughened or granular, but
with the three straighter edges marked by a smooth band. The
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