172 Rhodora [SEPTEMBER 
though there are a very few species of Diplazium in which one or the 
other breaks down. Such partially intermediate species occur, how- 
ever, throughout the ferns, and any attempt to unite the larger fern 
genera on such grounds would result in reducing such a family as the 
Polypodiaceae to a very few genera — possibly to a single genus. 
The scales of Asplenium consist of oblong cells, apparently nearly 
square in cross section, and the vertical interior cell-walls are dark 
colored and much thickened, while the superficial and marginal walls 
are very thin and transparent. This gives the scale, under the 
microscope, a clathrate appearance. In Athyrium, on the other hand, 
the typical scales are composed of elongated, more or less fibrous cells 
which are somewhat rounded in cross section, and all parts of the cell- 
wall are equally thickened, sometimes slightly, sometimes very greatly. 
Fig. 1. Structure of the stipe in the genera Athyrium and Diplazium. A-D, Athyrium 
angustum (Willd.) Presl. A, lower part of the stipe, X 5; B, upper end of the stipe, X 5; C, 
rachis of the frond; D, midrib of a pinna, X 10; E, F, Diplazium plantgginifolium (L.) 
(Brazilian material). E, stipe, X 10; F, midrib of the blade, X 10; G, H, D. grandifolium 
Sw. G, stipe, X 10; H, midrib of the blade, X 10. 
The result is that, under the microscope, there is no such contrast 
between walls and lumina as is seen in the scales of Asplenium. Similar 
scales áre found in Cystopteris, in Dryopteris, in Diplazium and in 
several other genera. In some species of Athyrium and in many 
species of Diplazium, the much reduced scales which occur along the 
rachis and veins of the frond, and especially in the axils of the pinnae, 
are somewhat clathrate, but the large basal scales, occurring on the 
rhizome and on the bases of the stipes are of the characteristic form 
just described. 
In Athyrium and Diplazium the structure of the stipe and the 
rachis is rather uniform (see fig. 1). Two large bundles enter the 
base of the stipe. These may be nearly parallel, but more com- 
monly they are somewhat inclined towards each other on the ab-axial 
