90 Rhodora [May 
Filiz mas (L.) Schott, D. marginalis (L.) Gray, D. spinulosa (O. F. 
Müll.) Kuntze, and D. cristata (L.) Gray, but not in D. Thelypteris 
(L.) Gray, nor in D. noveboracensis (L.) Gray. Furthermore I exam- 
ined Polystichum acrostichoides (Michx.) Schott, some species of 
Asplenium, Woodsia, Polypodium vulgare L., Adiantum pedatum L., 
Dicksonia punctilobula (Michx.) Gray, and Onoclea sensibilis L., but 
failed to find any trace of internal hairs in these. 
With respect to the structure of the leaf-segments (Fig. 1) D. 
marginalis shows a thick-walled epidermis, and the ventral sur- 
face is frequently papillose; the palisade tissue consists of two to 
three strata, very compact, covering open pneumatic tissue (P*), 
Fig. 1 Fig. 2 
Fig. 1. Cross-section of leaf-segment of Dryopteris marginalis; Ep., ventral, 
Ep,* dorsal epidermis; P palisade tissue; P* pneumatic tissue with glandular hair 
in intercellular space. X 240. 
Fig. 2. Two glandular hairs of same fern, from the pneumatic tissue. X 370. 
of which the intercellular spaces contain numerous, relatively large, 
glandular hairs. The lateral veins are embedded in the chloren- 
chyma, each surrounded by a large-celled, green parenchyma-sheath, 
inside of which is a thin-walled endodermis. In the midrib, on the 
other hand, is a strand of hypodermal collenchyma, which extends 
to the parenchyma-sheath; a strand of mechanical tissue is located 
in the margins. A like structure recurs in D. Filix-mas. 
The presence of these glandular hairs in certain species, and their 
absence from others within the genus Dryopteris, to which they are 
referred now, might indicate some generic distinction. Moreover 
