Christmas Fern 87 
Range. Nova Scotia and New Brunswick to Wisconsin, 
Iowa, Mississippi, and Florida. 
Polystichum acrostichoides (Michaux) Schott, Gen. Fil. 1834. 
Nephrodium acrostichoides Michaux, Fl. Bor. Am. 2: 267. 1803. 
As pidium acrostichoides Swartz, Syn. Fil. 44. 1806. 
Dryopteris acrostichoides Kuntze, Rey. Gen. Pl. 2: 812. 1891. 
Tue simplest leaf-blade of Polystichum acrostichoides seen is 
obcordate (PI. XVIII, Fig. 1). It contains a vein with two simple 
branches, one of which occupies each of the lobes. The leaf- 
blade becomes next more complexly lobed (Fig. 2@)), and its 
midvein lengthens, and sends out additional primary branches. 
The formation of pinnz is then carried out, and the venation 
develops in the manner usual in ferns with pinnate venation. 
The pinne form gradually, appearing first as mere lobes. 
At first the base of the leaf-blade is cuneate (Figs. 1, 2@0). 
It is rendered truncate before the first pair of pinnae become 
distinct (Fig. 4c), and then cordate (Fig. 3), by a broadening 
of these two pinne. 
In the early leaves the pinne are at first short and blunt, 
sometimes, in the very early leaves, even wedge-shaped or cuneate 
fan-shaped. They lengthen gradually, and become in highly 
developed leaves acute or sometimes acuminate. 
When newly formed, the pinnz in the very early leaves are 
apt to be cuneate at base and are sometimes nearly or quite 
equilateral, but a disposition to develop the upper side of the 
pinna at the expense of the lower is shown at a very early stage 
of the leaf-development. For some time this merely causes 
the pinna to appear one-sided, but finally it results in the pro- 
duction of the basal auricle seen in the mature leaves, which is 
an incipient pinnule, and is occupied by the superior basal 
