OBSERVATIONS ON THE VOLVOCACEAE. 333
There is yet another interesting behaviour on the part of these
organisms. Very early in the mornings the organisms are not so
noticeable, but a little later they swim actively all over the water.
Towards the middle of the day they recede below again, and towards
the evening they float up and form a sort of green mucilaginous
film on the surface. In this condition they are generally more
quiescent and often are dividing and forming daughter cells or
colonies.
Beach Pools
Sand is removed from the Madras Beach for building purposes and fairly deep hollows are formed in the sands very near the shore. During the monsoon seasons a large quantity of rain- water flows down from the Marina Road (which runs parallel to the seashore and is at a higher level than the sandy beach), and fills up these depressions in the sand. Again during the rainy weather the waves are rougher and some sea water also flows over the sandy shore into these pools. These pools, sometime after their formation, both during the summer monsoon and winter monsoon seasons, are soon peopled by large numbers of some member or members of the Volvocaceae. The most interesting feature of these pools is that the wet sand all round the edge of the pool to a distance of a foot or two is quite green. On lightly scraping the surface with a knife I found that the sand was green only near the surface. Microscopical examination of the wet sand revealed a large number of Chlamydomonas and other members of the Volvo- caceae swimming actively in the thin film of water surrounding the sand particles. Some of this green sand was collected by scraping the surface lightly and shaken with some water. The water became quite green leaving the sand in its normal colour. A drop of this green water examined under the microscope showed the organisms actively swimming about. I found this same preference for the wet banks in other similar situations also. The organisms prefer this situation probably because of better conditions of aeration. In another instance I found that a depression in the beach sands was merely wet at the bottom without any water in it. The surface of this depression was covered by a very thin layer of dry sand which was blown over by the wind. On removing this dry sand lightly with a knife I found the lower layer of sand wet and greenish. I also found that the greenness was confined only to a thin layer at the top and lower down the green colour was absent. I shook some of this green sand with water and found that its greenness was due to a large number of Chlamydomonadine cells which had lost their cilia and were quiescent.
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