LEAVITT: TRICHOMES OF ROOT. 
283 
It is noteworthy that when trichoblasts are formed the other epi¬ 
dermal cells do not put out hairs. In species characteristically tri- 
choblast-bearing, even when these organs are absent no root-hairs 
appear. 
It would seem that in certain groups and species of plants the 
capability of receiving and responding to the stimulus which initiates 
the formation of root-hairs is strictly localized in a portion of the der- 
matogen very near the extremity of the root trunk. Could we follow 
the protoplasmic movements within the cells of this region, the first 
visible response would probably be the transference of the nucleus 
from its usual central position to a station nearer one of the end 
walls. The first sign of activity manifest upon an inspection of the 
living tissues, however, is the existence of new transverse walls 
peculiarly situated, as already described. These operations in the 
meristematic zone, with their proper sequel in the further develop¬ 
ment of the trichoblasts, appear to be the only mode in which large 
numbers of plants are able to react structurally to the stimuli which 
call forth root-hairs. 
Distribution of Trichomes of the Second Type in Vascular 
Cryptogams and Angiosperms. 
General distribution. — Hair-cells of trichoblastic origin are found 
in the Schizaeaceae amongst Filices, in Equisetum, in Azolla, in 
Lycopodium and Phylloglossum, in Isoetes, and in Selaginella; in 
all the Helobieae examined, in nearly all the Glumiflorae examined, 
in some of the Spadiciflorae, in the Enantioblastae, in one genus of 
the Liliiflorae, in several orders of Scitamineae, in several terrestrial 
orchids among the Gynandrae; and finally in the Nymphaeaceae, 
where their occurrence is associated with an epidermal arrangement 
anomalous amongst Dicotyledons. 
Distribution of the second type; description of examples in the 
larger groups. —The origin, development, and anatomical characters 
of trichomes of this type are now to be described in detail in connec¬ 
tion with the groups and species in which they have been found to 
occur, either by myself or by observers who will be named. Species 
given without comment are species in which the hair-cells are prede¬ 
termined, but of which nothing further need be said. 
