436 MR. G. BREBNER ON THE ORIGIN OF THE 
On the Origin of the Filamentous Thallus of Dumontia filiformis. 
By Grorce BreBNer, late Marshall Scholar in Biological 
Research, Royal College of Science, London. (Communicated 
by Georce M. Murray, F.L.S.) 
[Read 1st March, 1894.] 
(Puates XXXV. & XXXVI.) 
A Government Grant was sanctioned by the Royal Society to 
enable the writer of the present paper to study the life-history 
of certain genera of marine alge. While these investigations 
were being pursued in the Clyde sea-area, an algal incrustation 
was noticed growing on Fucus serratus gathered at the Little 
Cumbrae, on the 30th November, 1892. Its colour was a very 
dark ruddy brown, almost like that of Petrocelis cruenta. This 
mMerustation was very variable in size and shape, attaining a 
diameter of 15 cm. to 2°5 cm., and was frequently found 
extending round from one surface of the host to the other 
without interruption. The first sections made showed the 
appearances presented in fig. 1; and the peculiar conceptacle- 
like conformation at a was specially noticed. The supposed 
conceptacle did not agree with any of those which are well known, 
and the incrustation was taken to be the imperfectly known 
Hematocelis fissurata, Crouan. Indeed it is somewhat difficult 
to believe the two things distinct after careful comparison 
of suitable preparations with the figure in the ‘Florule du 
Finistére ’*. 
A considerable number of sections were made from the fresh 
material, mounted in Dean’s medium, and laid aside pending 
further observations. It was not till March 1893 that the matter 
was cleared up, when this structure was found to be the attaching 
disk of Dumontia filiformis. The fact that this alga grows from a 
perennial “ basal disc” was published by J. Reinke in 1889T. 
He says :—“ The upright fruiting thallus arises from a basal dise 
which rests on the substratum. This disc is composed of closely 
packed vertical rows of cells, and resembles a Hildenbrandtia. 
Whereas the upright thallus dies down after the spores are shed, 
the basal disc is perennial and can put forth new thalli.” As 
far as could be ascertained, these are the only published obser- 
* Thid. pl. xix. fig. 127. 
t J. Reinke, ‘ Algenflora der westlichen Ostsee,’ Kiel, 1889. 
