242 THE AMERICAN MONTHLY [Sep 
from the multiplication in it of the very common Huglena, 
or some other of the unicellular alga, such as Protococcus. 
Frequently portions in similar localities appear pink or 
red, owing to the existence in them of immense numbers 
of some of the Daphnia or water-fleas. In the two cases 
now to be described, the colour, though extremely marked 
and characteristic, was the result of the presence of less 
common organisms. 
Early in October the ornamental water in the Botani- 
cal Gardens, Regent’s Park, appeared of an almost uni- 
form pale green. On close examination this was seen to 
be due to some minute bodies diffused through the water; 
they were not merely floating on the surface, but seemed 
about equally distributed at all visible depths. Every 
twig and thread of water-weed, etc., at the margin was 
covered with what looked to the unassisted eye like tiny 
green balls, while in the quiet corners and backwaters 
towards which the breeze was blowing, the same bodies 
were collected in such quantities as to resemble thick 
light-green paint. Uuder the microscope it was found 
that the tiny balls were of irregular outline, and consist- 
ed of small algw in colonies of various sizes, formed of 
more or less spherical groups. These were made up of 
very numerous individuals, oval or pear-shaped, so minute 
that the green colour noticeable in the aggregations was 
not distinguishable in them. The groups were hollow 
and surrounded by a thin Jayer of jelly or mucilage. In 
many cases there seemed to be spines radiating from the 
individuals, but these have no real existence, and the ap- 
pearance is probably due to the mucilage composed of 
the swollen outer cell-walls of the separate members not 
having yet entirely coalesced, 
The colonies, I think, have no motion within them- 
selves, but, being of nearly the same specific gravity as 
the water, are very readily moved about by any slight 
current, such as would be set up by wind, or by the sun 
