ASPLENIUM GRAVESII IN PENNSYLVANIA 121 
‘the same as characterize the two parents, showing that, 
as in another instance mentioned in the writer’s recent 
paper on rock ferns in this journal, the hybrid does not 
‘differ from the parents in soil preference.—Epear T. 
WHERRY, WASHINGTON, 
Recent Fern Literature. 
Glandular hairs are not infrequent on the outside of 
ferns, as of other plants, but it is probably news to most 
of us that they occur also inside. Dr. Theodor Holm 
has described and illustrated! such hairs which he found 
in the leaf-tissue of certain species of Dryopteris. If a 
cross-section of a leaf in these species be examined under 
the microscope, the tissue is found to be much more com- 
pact near the upper and lower surfaces. The cells there 
are closely contiguous; in the central part of the leaf. 
however, there are occasional air-spaces between them. 
In these spaces the glandular hairs are found. DeBary 
had long ago discovered such hairs in the ducts of the 
root-stock and the lower part of the petiole in Dryopteris 
Filiz-mas and D. spinulosa, but they seem not to have 
been hitherto observed in the leaf. Dr. Holm found 
them in D. Filiz-mas, D. marginalis, D. spinulosa and 
D. cristata, but not in D. Thelypleris nor D. noveboracen- 
sis, nor in representatives of seven other genera of our 
North American ferns which he examined. Nor are they 
known from any other plants whatsoever. Internal 
hairs have been noted in Pilularia and in four families of 
flowering plants, but in these cases they are not gland- 
ular. 
Dr. Holm points out that the presence of these sin- 
gular structures in certain species of the genus Dryopteris, 
as at present defined, and not in others, tends to confirm 
1 Holm, Theo. Internal glandular hairs in Dryopteris. Rhodora 22: 
89-91, figs. 1 and 2. May, 1920. 
