CONFERVOID FILAMENTS OF MOSSES. 57'J 
cellulose. It bears a considerable resemblance to the heterocysts of Nostoc (Collema- 
gonidium) and the so-called Nostochacese, considered by Braun * as the first appearance 
of vegetative permanent cells, — although he considers these to be formed by a cell divi- 
ding into two unequal halves, one of which remains permanent, and the other continues 
to segment. 
It has already been remarked that these filaments will soon cover a large space of t he 
ground in their neighbourhood with their branches, if they are p rmitted to grow unre- 
strained ; but after a time, particularly in damp, shady situations, the numerous brandies 
begin to crowd upon each other so as to form a compact mass of filaments (PL LVI1I. 
fig. 16) ; sometimes these intimately interlace, but more often they run upwards, parallel 
to one another (PI. LVIII. fig. 16, PL LVIL fig. 7). Very commonly these blanches 
are of nearly equal length, so that the surface on which they grow appears clothed with 
velvet. Sometimes, when they press closely upon one another laterally, they become 
hexagonal, and the cells of the lower portion, deprived of their due quantity of light, 
become nearly, and occasionally entirely, colourless. 
The foregoing description applies to confervoid filaments grown under circumstances 
favouring active vegetation, namely, under warmth and moisture, such as in the shade 
of walls, banks, and sides of ditches. The same can also be very readily produced art i- 
ficiaUy, by keeping them under a glass shade in a warm room, without direct sunlight 
But drought and cold produce very marked changes in their outward form and appear- 
ances, which I shall endeavour to describe. 
Under drought, more particularly during summer, the growth of the cells is much 
checked, and at the same time the cell-wall becomes much thicker. The cell-content s 
still growing, the chlorophyll-utricles crowd the interior, and press upon each other 
(PI LVII fig 11) Sometimes the cell-wall is itself dyed with chlorophyll, and some- 
what undefined from the contents, like the segmenting gonidia of Collema-* condition 
not very uncommon in the segmenting cell generally. This tendency to the blending oi 
the contents with the cell-wall I have endeavoured to show at PL LVIL fig. lib. It ,s 
very curious to observe the effects produced by alternations of weather upon the* hla- 
ments, illustrations of which may be procured artificially. Some of the cells are long, 
with few granules ; some are short, and the contents closely packed. Some have begun 
to branch! and become suddenly arrested in the process, the bulging part becommg 
covered with a dense cell-wall, precluding further growth m that direction. Some of 
these branches, encouraged by warmth and w^^n^ grown out into narrow 
elongated cells, so as to look something like roots (PL LVIL fig. 11 ft). A any part ol 
the cell is capable of bulging, and as any one of the cells can do so ^pend-^ of the 
other, and as the rate of growth of one cell is not limited by that ^^^^ 
easily be imagined how variable and tortuous may be the forms which these confenoid 
filanfents assume under the varying influences of our cHmate. Perhaps *: may be bes 
observed in those filaments which inhabit the bark of trees or dry walls, where the 
effect of the alternations of the seasons is more marked. - 
A very common effect which drought produces or increases is the development of a 
* Rejuvenescence in Nature, Ray Soc. 1853, p. 146. 
