On the Origin of the Filamentous Thallus of Dumontia filiformis
Journal of the Linnean Society of London Botany
A GOVERNMENT Grant was sanctioned by the Royal Society to enable the writer of the present paper t o study the life-history of certain genera of marine a l p . While these investigations were being pursued in the Clyde sea-area, an algal incrustation mas noticed growing on .Fucus serrnfus gathered a t the Little Cumbrae, on the 30th November, 1892. I t B colour was a very dark ruddy brown, almost like that of PetroceZis crzcelzta. This incrustation was very variable in size and shape, attaining
... nd shape, attaining a diameter of 1.8 em. t o 2.6 em., and was frequently found extending round from one surface of the host t o the other without interruption. The first sections iiiade showed the appearances presented in fig. 1 ; and the peculiar conceptaclelike conformation at a was specially noticed. The supposed conceptticle did not agree with any of those which are well known, and the incrustation was taken t o ba the imperfectly known HmnatoceZis$ssurafa, Crouan. Indeed it is somewhat difficult to believe the two things distinct after careful comparison of suitable preparations with the figure in the 'Florule d u PinistAre ' *. A considerable number of sections were made from the fresh material, mounted in Dean's medium, and laid aside pending further observations. It was not till March 1893 that the matter was cleared up, when this structure was fouud t o be the attaching disk ofDumontia$li$ormis. The fact that this alga grows from a perennial " basal disc " was published by J. Reinke in 1889T. H e says :-" The upright fruiting thallus arises from a basal disc which rests on the substratum. This disc is composed of closely packed vertical rows of cells, and resembles a I€iZdenbralzdtia. 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 tho only published obser-* Ibid. pl. xix. fig. 127 . t J. Beinke, ' Algenflora der westlichen Ostsec,' Kid, 1889.