A NEW GENUS OF PARASITIC ALGA. nag 311 
another, they form dense masses of radiating structure; such as are found in the mature 
plant. Under favourable circumstances, large numbers of such secondary disks are 
formed, and appear as elevated green patches and spots on the surface of the affected 
leaves. The primary disks cease to grow, and, after remaining for some time recog- 
nizable as small brownish patches on the surface of the epidermis of the new plant, 
gradually dry up and disappear. The relation of the primary and secondary disks to 
one another, and to the epidermis of the leaf, may sometimes be very clearly determined 
in transverse sections (Pl. XLIII. fig. 5). When the weather is dry the young plants, 
which are originally bright green, soon assume.an orange colour; and they then remain 
dormant and protected by the epidermis until favourable conditions of temperature and 
moisture rouse them to go on to increased growth and the ultimate development of the 
various forms of fructification. : | 
The various processes described in the previous pages seem to constitute the most 
important features in the life-history of this plant; and it now remains to consider some 
more general questions regarding it. As to its truly parasitic nature there can be little 
doubt. The situation of the mature plant, within the tissues of its host, and protected 
by a thick and highly cuticularized epidermis, would, even at first sight, lead to the 
conclusion that it was dependent on these tissues for its nourishment ; and this conclu- 
sion is confirmed by the destructive effects which it produces. Whilst its essential 
parasitism is thus rendered clear, it remains an open question, how far the Alga makes 
use of the organized materials of the tissues for its nutrition, and to what extent it pro- 
duces its prejudicial effects by merely appropriating inorganie elements of nutrition 
normally destined for the tissues of its host. That it acts, mainly at all events, in the 
latter way is rendered probable by the very various nature of the host plants on which 
specimens are found to occur; and much of the destructive effect which it produces may 
be ascribed to the large amount of water which it draws off whilst in active growth. 
In regard to the precise nature and alliances of this Alga, there are several points 
calling for consideration. So far as the vegetative growth is concerned, it agrees 
very closely with the genus Coleochete, the primary disks resembling the disks of 
C. scutata, whilst the secondary ones approach in characters those of some of the 
more loosely branched species. There is, however, an entire absence of the bristles 
characteristic of Coleochete. When we come to consider the reproductive organs, the 
resemblance ceases, and very striking differences make their appearance. The asexual 
zoospores, in place of being produced indifferently in any cells of the disk, are here deve- 
loped only on highly specialized filaments; and the sexual fructification, in place of 
being a well-developed carpospore, the result of fertilization by motile antherozoids, is 
rather an oospore than a carpospore, and is the result of fertilization by means of anthe- 
ridial filaments. There is never a formation of true carpospores, although in many cases 
a tendency to such formation is indicated by the investment of the fertilized oogonium 
by a mass of cellular filaments. So in regard to the ultimate development of the sexual 
process, in place of the formation of a cellular mass, the individual cells of which give 
origin to zoospores, there is here an immediate resolution of the contents of the oospore 
2x 2 
