LEAVITT: TRICHOMES OE ROOT. 
307 
a few are more or less xerophytic. At the same time many aquatic 
plants, distributed amongst several of the larger groups of Mono¬ 
cotyledons and throughout the Dicotyledons, are without tricho- 
blastic formations. 
Granting that the character may have some phylogenetic sig¬ 
nificance, it is interesting to note that on the one side the peculiar 
structure of the piliferous layers so widely present in Monocotyle¬ 
dons is like that prevailing in the higher vascular Cryptogams; and 
that on the other side a structural resemblance may be traced to the 
outer cortical layer of the root in many Dicotyledons. In case the 
Angiosperms are from a Gymnospermous ancestry, the question 
which of the conditions found in the radical epidermis in the two 
divisions of the group is the original one, is one to which no answer 
can be given. The trichoblastic condition obtaining in Monocotyle¬ 
dons might be derived from that seen in Dicotyledons by denudation 
of the trunk proper, as in Nymphaea. At the present time, how¬ 
ever, when the origin of flowering plants is obscure, it is pertinent 
to remark the dissimilarity of Angiospermae and Gymnospermae in 
respect to the organization of the apical region of the root, and, 
in contrast, the agreement of Angiospermae with certain Pteri- 
dophyta in this particular; and to call attention to the additional 
fact that the structure of the primary integument of the root-trunk 
obtaining so extensively in the branch of the Angiosperms, viz., the 
Monocotyledons, which on the whole seems to be the more primi¬ 
tive, is closely similar to that prevailing amongst the higher Pteri- 
dophytes in the well marked feature which has been dwelt upon 
at length in this paper. 
Many of the plants used in carrying out this research were 
seedlings. For seeds and in some instances for growing plants or 
preserved material I am greatly indebted to Sir W. T. Thiselton- 
Dyer, Prof. A. Engier, Prof. W. F. Ganong and Mr. E. J. Canning 
of Smith college, Mr. C. D. Beadle of Biltmore herbarium, Mrs. 
A. P. Taylor of Thomasville, Ga., Mr. Robert Cameron of the 
Harvard botanic garden, Dr. B. L. Robinson, and my associate, Mr. 
A. A. Eaton. The work has been made possible by the ample 
facilities of every kind provided by Mr. Oakes Ames. 
