STRUCTURE OF HILDENBRANDTIA FLUVIATILIS. 227 
Subsequent Observations.—On examining the little light-coloured 
papille on Hildenbrandtia fluviatilis again, I can come to no other 
conclusion than that they are the conceptacles, for, besides differing 
slightly in structure from the rest of the thalloid expansion, there is 
nothing else on it that I cau see to represent the fructification of the 
species but these papille. 
The conceptacle, then, in Hildenbrandtia fluviatilis rises on the dark- 
red layer of cells, which forms the thallus as a pimple of a lighter 
colour than the thallus, and losing almost all its redness as it increases 
in size, at length arrives at about 45th of an inch in diameter (Fig. 6). 
In form it may be circular, oval, or irregularly curvilinear in outline. 
The summit then opens, and the columns of cells of which the crust 
is composed fall back so as to give a crateriform hollow with sloping 
sides (Fig. 7). Cracks then extend outwards from this cavity, and 
as the latter enlarges so the columnar structure falls away (Fig. 8), 
until it is diminished to a little white border, which forms the line of 
demarcation between the red thallus and the enlarged crateriform 
hollow within, now occupying nearly the whole of the base of the ori- 
ginal papilla (Fig. 9). Tt is the running together of these papillæ, and 
the subsequent desquamation just mentioned, which gives the sca- 
brous appearance to the thallus above described. 
columns, which I have figured, are composed of 6-10 cells, 
piled one upon another, and a single or crucial division frequently ex- 
tends downwards from the surface to the third cell inclusively, which 
thus diminishes the size of the cells, and multiplies the number of co- 
lumns peripherally (Fig. 4). Each cell, large and small, presents a 
nucleus, and the other cell-contents lose their red colour in proportion 
as the columns are distant from the base of the papilla or conceptacle. 
I also observed this time that there appeared to be a layer or group 
of cells still a little larger than those of the columns, forming the bottom 
of the, so to write, crateriform cavity, whose contents respectively, 
void of red colour, but tinted a little yellowish, bore a very cireum- 
scribed, spore-like appearance (Fig. 2), while in both among the cells 
of this group and among those of the columns, there were several 
empty ones. Had the contents of these left them in the form of fruc- 
tifying elements ? 
On crushing the conceptacles under the microscope, a few zoospores 
made their appearance, of the colour of the contents of the supposed 
Q 2 
