94 S lurch . — Harveyella mirabilis ( Schmitz & Reinke). 
smaller than the other cells of the gonimoblast. The terminal 
cells of these filaments develop into spores, which are at 
first small and oval in shape; but when mature they are 
usually oval, though occasionally they are almost spherical. 
They are set free by the breaking away of a portion of the 
periphery, which in the mature cystocarpic plant is only 
attached to the central tissue by the very long and narrow 
cells. 
The spores stain rapidly with Hoffmann’s blue, as do also 
the cells of the erect gonimoblast-filaments, those nearest 
the spores staining most deeply. The nuclei of the spores 
stain well. The cells of the horizontal filaments of the 
gonimoblast stain deeply when young, but as they become 
older they only stain very slightly, resembling the ordinary 
thallus-cells. 
Thus the cystocarp, when mature, consists of a much- 
branched gonimoblast derived from the product of the fusions 
of the auxiliary cell. This gonimoblast consists of filaments 
growing in all directions horizontally among the thallus- 
tissue, until the ramifications spread throughout almost the 
whole of the hemispherical cushion-like part of the plant 
which is outside the host, just beneath the peripheral layer, 
which is borne on very long and narrow vegetative cells. 
From these horizontal filaments arise erect much-branched 
tufts of gonimoblast-filaments, the terminal cells of which are 
developed into spores. 
When fully mature, the whole plant — except the part 
inside the host — is cystocarpic ; that is to say, there is 
a layer of erect gonimoblast-filaments bearing spores ex- 
tending round the whole hemispherical external frond, just 
beneath the peripheral layer. This cystocarp is not con- 
tained in any special coat or wall, but is bounded on the 
exterior only by the slightly-modified ordinary peripheral 
cells, and on the inner side by the central tissue of the 
thallus. 
Taking the view of an antithetic alternation in the life- 
history of the Florideae, it is worthy of note that in Harveyella 
