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. 

 Aspidium acrostichoides Swartz, Syn. Fil. 44. 1806. 

 Dryopteris acrostichoides Kuntze, Rev. Gen. PI. 2: 812. 1891. 



THE simplest leaf-blade of Polystichum acrostichoides seen is 

 obcordate (PL XVIII, Fig. i). 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 a 5), and its 

 midvein lengthens, and sends out additional primary branches. 

 The formation of pinnae is then carried out, and the venation 

 develops in the manner usual in ferns with pinnate venation. 



The pinnae form gradually, appearing first as mere lobes. 



At first the base of the leaf- blade is cuneate (Figs, i, 2 a b). 

 It is rendered truncate before the first pair of pinnae become 

 distinct (Fig. 4^), and then cordate (Fig. 3), by a broadening 

 of these two pinnae. 



In the early leaves the pinnae 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 pinnae 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 



