100 MR. H. M. WARD ON THE STRUCTURE, DEVELOPMENT, 
distinguished from the more casual occurrence of foreign Algæ, Fungi, &c. so usual оп 
all such patches on leaves in the tropics, and especially on such Algæ as these, the hairs 
of which act readily as traps to catch any wind-blown or washed spores «сс. 
But the more or less accidental invasion of so widely spread a network would have 
excited little remark had it not been noted that definite changes in the organization of 
the Algal thallus accompany and follow from the invasion, and that, in proportion as the 
Fungus invests the Alga, the cells of the latter are affected the more. Nor is this all; 
the Fungus in its turn flourishes more luxuriantly as its invasion and, as will be shown, 
depredations on the thallus proceed. 
The earlier inroads of the mycelium consist simply in the wandering of the hyphze along 
and across the margins of the thallus, in ordinary cases ; but later the filaments branch, 
anastomose, and rapidly spread over the surface, at length forming a superficial investment, 
often of some complexity. In numerous if not in all cases the Fungal threads follow 
the lines of cell-division more especially, and may be readily recognized by their brown 
tint as so doing (Pl. ХХІ. figs. 59 & 60). Having produced а tolerably complete investing 
web, so to speak, the mycelium soon afterwards commences to produce the first of its two 
kinds of fruit-body (figs. 60 & 64 &c.), a structure consisting of a capsule of matted 
hyphee, in the interior of which arise simple, naked stylospores—a pycnidium in fact. The 
second, higher form of fruit-body, a perithecium containing asci, does not rise till 
later, as will be described shortly. 
Now the point of importance to this inquiry is, that these two compound fruit-bodies, 
the pyenids and perithecia, only arise from the mycelium after it has successfully invaded 
tlie Alga-thallus; in no case, after repeated and long-continued search, have I found the 
fruit-bodies on the mycelium as it overruns the leaf. Conidia and hyphæ occur in plenty, 
both on leaf and thallus, but no pycnids or perithecia, until some progress has been made 
on and in the Algal thallus. 
The investing mycelium, as said, frequently forms masses of conidia; and when all 
three forms of reproductive organs occur, they appear in this order—conidia, then pyenids 
(often crowded in dense clusters, see fig. 62), and finally the perithecia, which seem to be 
produeed only after great vigour has been attained by the Fungus feeding on the Alga. 
If a thallus of the type described earlier (p. 88) as grey, or greenish grey, be examined 
en face, it becomes evident that it differs from the first (orange-red or green) type chiefly 
in that the investing mycelium of the Fungus now under consideration has commenced 
to attack it; this is shown in fig. 62, where the mycelium has already made considerable 
advances, causing the orange-red or green cell-contents to become merged in a cloudy 
matrix. Іп this case, also, there are several groups of pycnidia formed. In figs. 57 & 58, 
which represent portions more highly magnified, the same events come out more dis- 
tinctly, and again in figs. 59 & 60. 
_ When this stage is reached it becomes evident that the cells of the thallus are affected 
in two ways: first, their mode and rapidity of division is interfered with ; and, secondly, 
their cell-contents are more or less injured or changed. 16 frequently happens that, as 
in fig. 58, the cells attain a much smaller volume before dividing, and the rapidly fol- 
lowing division-walls remain parallel to the circumference, until the power of growth 
seems to become arrested as the mycelial filaments extend over the cells; in such cases, 
