582 Acton . — Botrydina vulgaris , Brdbisson, 
Working on this hypothesis, the material was carefully examined to see 
if any connexion could be traced between the Botrydina and the fungal 
hyphae occurring in the mucilage in which it was embedded. After much 
material had been examined, two or three specimens were found (40-50 /x in 
diameter) in which a hypha could be seen in direct continuity with the 
envelope (PI. XLIV, Figs. 2 and 3). Very few specimens were seen showing 
this connexion, so that if the envelope were formed by a proliferation of a 
fungus hypha it must lose all connexion with it at an early stage. A re- 
examination of the material brought to light a number of early stages in 
which the connexion of the globular bodies with the fungus could clearly 
be seen (Figs. 4 and 5). There is thus no doubt that the colourless 
envelope is formed by investing fungal hyphae. 
The Structure and Arrangement of the Green Cells. 
On gently crushing the globular structures which had been mounted 
in water, numerous green cells escaped into the surrounding fluid. These 
proved to be a unicellular green alga. The cells were usually elliptical in 
form, about 6-8 /x in length by 3-4 \x in breadth, though many of them 
were flattened and angular, and others curiously twisted (Fig. 6 b). The 
chloroplast was parietal, but did not extend over the whole cell, one side 
of the cell being colourless. There was a single pyrenoid in the centre 
of the chloroplast. In the colourless portion of the cell, several highly 
refractive granules were frequently present (Fig. 6 c). The nature of 
these was not determined. They gave no reaction for starch, oil, or 
sulphur. 
The alga multiplied by oblique fission, freshly liberated cells often 
showing this condition (Fig. 6 a). 
Sections were then cut in paraffin to determine the morphological 
relationships of the alga and fungus. Those sections stained in a one per 
cent, solution of acid-fuchsin gave the best results. The inner structure of 
the thallus varied in different specimens, and depended on whether the alga 
or the fungus was predominant, and not on the size or age of the thallus. 
In some specimens the interior was entirely filled with algal cells embedded 
in mucilage (Fig. 7), the fungus forming an investing sheath ; while in 
others the interior was filled with cells similar to those of the outer envelope, 
but with intercellular spaces, so that here the fungus did not form a sheath, 
but a pseudo-parenchymatous tissue, to the intercellular spaces of which the 
alga was restricted (Fig. 8). The crowding of the alga into the intercellular 
spaces would account for the flattened and distorted forms mentioned 
earlier. Stages intermediate between these conditions were present. Pos- 
sibly a condition where a tissue is present would result from an earlier 
condition similar to that shown in Fig. 5, where the envelopes from a group 
of young thalli are confluent and the fungus seems to be predominant. 
