— 66 — 
and “reddish-brown” have cells which are “especially distinctly collenchymatous, 
while the more vigorous green forms .... have thin-walled cells which 
are indistinctly collenchymatous.” 
The writer has found the following conditions in typical forms of the species, 
such as th£ specimens from the vicinity of Berlin, collected by Osterwald and 
distributed by Schiffner (Hep. Europ. Exsic. 57), or the specimens from Nova 
Scotia, collected by Nichols (No. 1376). The marginal row of cells is distinct 
all the way round (except at the very base) and in the apical portion (Plate II, 
fig. 8) stands in especially sharp contrast to the cells just within; toward the 
base the contrast becomes less striking. The cells average about 40,11 in both 
radial and tangential dimensions, but the latter often vary between 30 and 50,11. 
The outer walls are sometimes 8,u thick; the radial walls appear almost as thick 
(as the figure shows), but careful focusing shows a large thin place in each; the 
inner walls are somewhat less thickened and present the appearance of having 
large pointed trigones with concave sides. The cells just within the marginal 
cells average only 20^ in diameter and are therefore only a quarter the size of 
the marginal cells in surface extent. Their walls (except those common to the 
marginal cells) are very slightly thickened, and it is often difficult to say whether 
trigones are present or not; even in extreme cases the trigones are minute with 
strongly concave sides. Toward the base of the leaf the cells gradually increase 
in size and especially in length, the median cells measuring about 40X28,11; their 
walls are even thinner than those of the submarginal cells, and their trigones, 
although no larger, appear somewhat more distinct. The cuticle is everywhere 
verruculose or striolate-verruculose. 
In the var. gracillima , as represented by specimens collected in the Vosges 
Mountains by Muller and distributed by Schiffner (Hep. Europ. Exsic. 361), 
the conditions are very different (Plate II, fig. 9). There is no contrast, either 
in size or structure, between the marginal and submarginal cells, both averaging 
about 22/j, in diameter; toward the base the cells become longer but scarcely 
wider, the median cells averaging about 29X22,1*. The walls are everywhere 
slightly thickened but minute trigones with concave sides can often be demon- 
strated; the cuticle is smooth or nearly so throughout. 
Under certain circumstances the more “collenchymatous” appearance noted 
by Hesselbo presents itself. The specimens collected by Underwood at Auburn, 
Alabama, and distributed by Miss Haynes (Amer. Hepat. 61) represent this 
condition. According to the label they were found “on rocks in a ravine,” but 
the rocks were either covered with earth or much disintegrated, because the 
substratum of the plants is in the form of minute granules loosely held together. 
The plants are small and deeply pigmented and seem to have grown in an exposed 
locality. Their leaves are distinctly bordered, just as in the typical form, but 
the contrast in size between the marginal and submarginal cells is somewhat 
less, the marginal cells averaging only 3 2/j, in diameter and the submarginal i8ju. 
The smaller size of the marginal cells may be associated with the fact that the 
leaves themselves are distinctly smaller than in the usual form of the species. 
With regard to the cell-walls the marginal cells present no aberrant features, 
