3 2 6 
Cleland.—The Cytology and Life-history of 
Trichomes may continue the axis of the parent filament (Text-fig. 2,^), 
but more usually they are developed at one side of the median line of the 
terminal cell (Text-fig. 2,e). Each trichome is equipped with a nucleus, 
but has no chromatophore. After the trichome cell is cut off, it grows 
very rapidly and soon becomes fifty or more times as long as broad. At 
its distal end there is a quantity of cytoplasm in which lies the nucleus. 
The rest of the hair appears to be empty. After it has reached maturity, 
the base of the hair begins to gelatinize and a new trichome is developed 
to take its place. 
It is important to notice, in relation to the development of the 
Text-fig. 2. Method of growth in a vegetative tuft. a. Lateral budding to form a side-branch. 
b. Terminal budding to form a trichome. c. False appearance of dichotomy, d. Trichome developed 
on the median line. e. Trichome developed to one side of the median line. f. Looped central 
strand filament, x 700. 
chromatophore, to be described later, that the growth of the assimilative 
tuft is limited and that this limit is reached very close to the growing apex 
of the plant. Cells, therefore, which but a short way behind the apex are 
terminal cells of filaments, will contiuue to be terminal all through the 
history of the plant. The growth in thickness of the thallus, as it becomes 
older, is due to increase in the number of central strands ; and the increase 
in assimilative structure which goes with this enlargement is due entirely to 
the development of new or secondary filaments, either from old tufts or 
from active strands of the central region. 
