332 THE JOURNAL OF INDIAN BOTANY.
Occurrence of the Volvocaceae
The members of this group occur in different kinds of situation ; rain-water pools, permanent pools, ponds, ditches, water tubs, paddy- fields, streams, and tanks. They occur throughout the year but attain their greatest development and occur as dominant forms only during the summer monsoon season in the many small rain-water pools that are then formed. During the colder season, though they occur in various situations, they never reach the abundance noticeable in the rain-water pools formed during the summer season, but occur only as subordinate forms, though occasionally Volvox or Pleodorina, may occur for very brief periods as dominant forms in certain waters. I shall now take up the summer monsoon rain-water pools as being the more interesting of the two.
Summer rain-water pools
After the first few summer showers, the water collected in the various rain-water pools all over the place, begins to turn green. And an examination of a drop of this green water shows countless numbers of some member or members of the Volvocaceae. The following genera have been collected by me in these pools during the summer monsoon season : — Chlamydomonas, Carteria, Gonium, Pandorina, Eudorina, and Volvox. All excepting Volvox were found in great abundance.
The behaviour of these organisms in the summer rain-water pools is rather interesting. As was pointed out above, the rains during this season are small in quantity and occur at frequent intervals. During the rainless days succeeding a rainy day the water level in the pool goes down gradually and when almost near the bottom a fresh rain comes in and the level of the water goes up once more ; and this process is repeated again and again throughout the season.
A few days after the filling up of a pool, the level goes down somewhat and a greenish scum is noticeable on the surface which soon extends deeper and becomes greener. And an examination of a drop of this green water shows large numbers of some member or members of the Volvocaceae (mixed up of course with some diatoms, and some other plankton algae, such as Scencdesmus, Coelastram, etc.). As the level goes down, the water gets even more green in colour. But when the pool gets filled up in the next rain, the green colour does not get thinner through dilution but disappears totally. After the level goes down somewhat again as before, a thin green scum is formed and as the level goes down still more the colour deepens and the organisms are seen in large numbers as before. And this interest- ing process is repeated again and again.
