184
SAND-GRAINS AGGLUTINATED INTO
FLOCCULENT MASSES BY SMALL ALGAE.
By D. J. SCOURFIELD, I.S.O., F.L.S., Etc.
(With Text Figures.)
SHORTLY after the delivery of my Presidential Address to
this Club in March, 1927, dealing with the subject of
certain field phenomena due directly to microscopic organisms,1
I met with another and very excellent example of such an
occurrence in the Epping Forest district. Along a considerable
portion of the sandy margin of the large piece of water on Leyton
Flats usually known as the Hollow Pond I noticed numerous
small patches and some long lines from one to three inches in
width of a pale yellowish-green colour which, when touched,
appeared to consist of small masses (up to about one-tenth inch)
of some flocculent material. The patches were in slight hollows
in the sand, very close to the water's edge, and the lines were
actually at the margin, both being evidently produced by the
action of the ripples upon the seemingly floccose matter. I
naturally thought that the latter would prove to be merely
vegetable debris of some kind, and I was much surprised to find
when the material was examined under the microscope that each
little flocculent mass consisted of small sand-grains held together
in some way that was not at first evident. Scattered about
among the sand-grains, however, were large numbers of minute
green bodies, all of which under higher magnification proved to
be groups of the unicellular alga Scenedesmus antennatus
Brebisson, and I gradually convinced myself that these were,
if not possibly the sole, certainly the principal agents responsible
for the agglutination of the sand-grains into masses. The
justification for this conclusion will, I think, be admitted from
what follows.
When the little masses of sand-grains were broken up in a
watch-glass by means of a camel-hair brush it was found that,
although some of the S. antennatus groups and individual cells
were detached, most of them were still adhering to the sand-
grains and that the latter were not as a rule even yet completely
1 Essex Naturalist, vol. xxii., p. 5.