A NEW GENUS OF PARASITIC ALGA. | 307 
servation of the parasite under these circumstances, the amount of it surviving from one 
season to another would be comparatively small. 
. Such an arrangement is, however, provided in the sexual fructification. During the 
height of the rains, and whilst vegetative growth is actively progressing, only the asexual 
fructification is produced; but subsequently the sexual form begins to appear, and, 
gradually increasing in abundance, eventually more or less completely replaces it. The 
sexual organs, in place of taking origin from the aerial filaments, are developed on 
those of the subepidermal disk. These filaments, in place of containing an abundance 
of brilliant green protoplasm, as at first, begin to assume a yellowish tint, and ultimately 
come to contain only masses of globules and granules of as vivid an orange colour as that of 
the contents of the aerial branches (Plate XLII. figs. 9, 10). Whilst this change of colour 
is taking place, the contents also become greatly condensed and contracted, so as in 
many cases to be reduced to one or two isolated masses, or to a mere band along the 
centre of the cell. Their coarsely granular consistence also disappears; and a number of 
separate globules of large size and oily aspect are ultimately formed. 
Whilst these changes are advancing, the organs destined for sexual fructification 
begin to appear. Certain of the filaments, in place of, as before, continuing to grow by 
a process of dichotomous division, resulting in the formation of two nearly similar 
branches, give origin to only one filament at the site of division, whilst the other member 
of the dichotomy, in place of elongating, swells up into an obovate dilatation (Pl. XLII. 
fig. 11). This is sometimes sessile, but is generally situated on a short process of the 
mother cell. A septum now forms at the base of. the dilatation ; and the latter rapidly 
increases in size, and becomes filled with a great accumulation of orange protoplasm. 
The new cell now appears as a large thick-walled sac inserted between the neighbouring 
filaments of the disk, which are displaced laterally by its growth, and, curving along its 
margins, come again into contact at its distal extremity. The thickness of the cell-wall is 
very considerable, amounting in many cases to as much as 0:004 millim., and frequently 
shows distinct evidences of stratification. "The cells, when mature, vary considerably in 
size ; but average specimens may measure about 0-0625 x 0:0415 millim. Due to the dense 
nature of the disk, to its subepidermal site, and to the fact that, when detached from the 
leaf, only retrograde changes, tending to a recurrence to pure vegetative growth, occur 
in the developing fructification, I have been unable continuously to follow out the 
further steps in the development of these cells, or oogonia as they now are. In so far, 
however, as very numerous examinations of separate specimens are capable of throwing 
light on the matter, the following appears to be the order of events. The contents ot 
the oogonia, which were at first in close relation to the walls of the cell, become gradu- 
ally removed from them as the cell enlarges, and form an oospheric mass, separated from 
its case by a distinct interval, save towards the basal extremity, immediately over the 
septum dividing the oogonium from its mother cell. Whilst these changes have been 
occurring in the oogonia, numerous slender-branched filaments have arisen from the 
neighbouring cells of the disk. Some of these become dilated at the extremity ; and the 
large terminal cell becomes applied and closely adherent to an oogonium (Pl. XLII. 
fig. 12). These filaments appear, as a rule, to arise from the under surface of the disk ; 
