286 THALLOPHFTES. 
FORMS CONTAINING CHLOROPHYLL. 
These are all submerged water-plants, the vegetative and reproductive organs 
of which have a well-marked tendency to clothe themselves with a peculiar cortex. 
This is especially remarkable in the genus C/iara, and it will be described in detail 
hereafter when that genus is under consideration. It is also very evident in the 
Ceramiacese, and but rudimentary in the Coleochaetese, where it is confined to the 
fruit. Side by side with forms possessing this cortex, there are others, very nearly 
related, which do not possess it. 
In all the plants belonging to this group the fruit is small in proportion to the 
thallus which bears it, and the alternation of generations which finds its expression 
in the formation of the fruit is therefore 
not very clearly marked. 
A. The CoLEOCHiEXE^. 
The carpogonium is unicellular with a long 
trichogyne opening at its apex. Fertilisation 
is effected by antherozoids which are formed 
either in special small branches or in the cells 
of a filament which have undergone division. 
In the basal portion of the fertilised carpogo- 
nium there is a cell which grows considerably, 
and becomes invested by outgrowths derived 
from neighbouring cells. In the next period 
of vegetation it gives rise to numerous carpo- 
spores in the form of zoospores. 
The Coleochseteae ^ are small (about 1-2 
mm.) fresh- water Algae, of a bright green 
colour and constructed of branched rows of 
cells, attached in standing or slowly-running^ 
water to the submerged parts of other plants 
{e,g. Equisetum), and forming circular closely- 
attached or cushion-like discs. Their chloro- 
phyll assumes the form of parietal plates or 
of large granules. The name of the genus 
Coleochsete (sheath-hair) is due to the circum- 
stance that certain cells of the thallus bear 
lateral colourless bristles fixed in narrow 
sheaths (Fig. 186, A, h). If the phenomena 
of growth of the difi'erent species are com- 
pared, two extreme cases are seen, connected 
by transitional forms. The one extreme is 
formed by C. di'vergens, which, as it developes 
from the spore, produces first of all creeping 
from these spring ascending articulated 
Fig. 186.—^ an asexual plant of Coleochcete sohtta ( x 250) ; 
B a piece of a similar disc ; the letters a-g indicate the suc- 
cessive dichotomous branchings of the terminal cells (after 
Pringsheim). 
irregularly-branched articulated threads 
branches which are also irregularly branched; the whole thallus does not assume 
any definite form. In C. pul'vinata, on the contrary, the thallus forms a hemi- 
^ Pringsheim in Jahrbuch für wissenschaftliche Botanik, vol. II. p. i. 
