154 
structure and life-history of the plant. Owing to unforeseen 
circumstances the investigation has not been carried out in the 
detail that was intended, but from 1908 to the end of 1910 the 
Weymouth neighbourhood has been visited nine times, and the 
growth of the plant as it occurs there has been followed during 
all seasons of the year. 
- Although a certain number of specimens are found during the 
summer, Colpomenia in these latitudes is essentially a winter plant. 
n a general way it commences growth in the autumn and 
disappears in late spring or early summer. The account given 
If the larger rock-pools are carefully searched during the begin- 
ning of September, a number of small Colpomenia plants will be 
found attached to the submerged and shaded parts of such stout 
algae as Halopithys pinastroides and Cystoseira granuluta. At this 
date, the spherical thalli are not more than 1 or 2 mm, in diameter, 
and are thus apt to be overlooked. By the end of the month a 
marked increase in the size and number of the thalli is noticeable, 
and specimens a centimetre or more in diameter are of frequent 
occurrence. During October and November the growth is very 
rapid, and by the end of the latter month many specimens will 
have reached the average size of the winter-growth, namely 
14-2 inches in diameter. 
In late autumn Colpomenia forms a most conspicuous feature of 
the lower part of the shore. It occurs in pools, and on rocks from 
about half-tide level downwards ; it is also found in the sub-littoral 
region, namely in the shallow water immediately below the low-tide 
limit. On rocks the plant is generally epiphytic, growing attached 
to Chondrus, Halopithys, Corallina, and other algae, but specimens 
attached directly to the rock may also be found. In the sub-littoral 
region it is-likewise epiphytic, and, if the locality be sheltered, 
it often occurs in great profusion, In pools it is even more 
abundant, the larger specimens crowding the stems of Halopithys, 
Cystoseira, and Fucus serratus; and the smaller ones being foun 
on species of Ceramium, Polysiphonia, and many other algae, The 
Colpomenia-thalli act as buoys to their host-plants, and, when 
attached to slender species such as Ceramium, frequently cause 
damage to the shoots, in that they sooner or later break away carry- 
ing with them a portion of the slender frond. The conditions of 
rock-pools resemble those of the sub-littoral region rather than the 
littoral ; and, though Colpomenia flourishes when exposed to the 
air as a low-littoral plant, it is always larger and more abundant 
when growing in pools or in shallow-water, 
