286 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
as it meets the outer wall of the mother cell. The somewhat older 
trichoblasts are wedge-shaped (pi. 16, fig. 13), and this form is seen 
in the trichome (pi. 16, fig. 15). In superficial view, at a point 
immediately back of the cap, the trichoblasts appear strongly convex 
laterally and somewhat wider than the atrichomic cells (pi. 16, fig. 
14 ). At times the piliferous and non-piliferous elements alternate 
regularly; at other times the trichomes are found scattered irreg¬ 
ularly. The hair is at first directed obliquely toward the apex of 
the root. 
All the species seen agree closely in the character of their tri¬ 
chomes. The following were examined : Equisetum arvense , E. 
debile , E. diffitsum, E. hyemale , E. limosum , E. litorale, E. ram- 
osissi??ium, E. scirpoides , E. variegatum. 
Lycopodinae. 
Lycopodium. — Nageli and Leitgeb 1 describe the origin of the 
trichomes in Lycopodium clavatum. From this account, which is 
illustrated by diagrammatic figures, we learn that the trichomes first 
appear under the root-cap in the form of wedge-shaped portions cut 
off by oblique walls from the basal half of the young epidermal cells. 
These wedge-shaped cells divide from one to three times, by walls 
at right angles to the oblique wall, to form from 2 to 4 adjacent cells, 
each of which grows out into a root-hair, while the remaining part 
of the original epidermal cell at once elongates. Sometimes only a 
corner of the epidermal cell is cut off, in which case but one hair is 
formed. 
The same history is to be given for several native species of 
Lycopodium which I have examined ; viz., for L. annotinum , X. 
dendroideum , L. lucidulum , X. obscurum , X. sabinaefolium , and 
X. sitchense. Lycopodium inundatum , however, departs from the 
usual type. This species and X. lucidulum are now to be described 
in detail, with the reproduction of drawings from nature. 
Lycopodium inundatum (pi. 16, fig. 16-19).— In the develop¬ 
ment of the epidermis the differentiation of the trichomes begins 
within a veiy short distance of the apex. In a typical case the first 
1 Nageli & Leitgeb : Enfktehung unci wachsthum der wurzeln. C. Nageli's 
Beitriige zur wissenschaftlichen botanik, 4 (1868). 
