4A MR. G. BREBNER ON THE ORIGIN OF THE 
field of investigation, viz. the secretion of enzymes by marine 
plants. 
It is also interesting to note how the basal thallus by localized 
vigorous growth creeps over itself, as it were, and becomes 
several layers thick (fig. 1, er.th.). When the annual thallus 
dies down, its base, which is immersed in the perennial part, 
persists and is subsequently imbedded by the overlapping of the 
latter (fig. 1, ¢). The immersed portion is frequently not developed 
peripherally in the candelabra-like manner of the free part, but 
in one or two cases sections show the former having precisely the 
same structure as the latter. 
M. Mobius has figured the relation of the exotic little Am- 
phiroa (brasiliana?) to its attaching disc*, but as the upright 
thallus is evidently not developed in any way analogous to the 
case just considered, it does not require more than passing 
mention here. 
In September 1893 the writer learnt from Prof. Harvey Gibson, 
of Liverpool, that he had found the “ basal dises” of Dumontia filt- 
Sormis growing on Laminaria hyperborea, and that he had traced 
the most important points in the origin of the ordinary thallus from 
the “ basal disc ” as early as 1889. As Prof. Gibson had not yet 
published his observations, although intending to do so sooner or 
later, he courteously waived his claim to priority on learning that 
the present paper, based on entirely independent observations, 
was in progress. 
Summary. 
(1) D. jfiliformis has a creeping basal thallus by which it 
adheres to the substratum. 
(2) The creeping thallus is perennial and, when epiphytic 
(parasitic ?), is attached to its host by plugs of tissue which cause 
marked disintegration of the cells of the host. 
(8) The ordinary filiform thallus owes its origin to the inter- 
calary transverse septation of the articulations of certain branches 
of the creeping thallus. The group of active filaments may be 
endogenous or exogenous, and the order in which the rows of 
cells become specialized is generally centrifugal, i.e. certain fila- 
ments begin to divide in an intercalary manner and the adjoining 
filaments follow suit, the most recently divided being most 
peripheral. 
* ‘ Hedwigia,’ 1889, Taf. xi. figs. 15 and 16. 
