1918.] jST. Aninandai.e: TIic I aU Lake. 3 



I have already alluded to the impossibiUty of stating the exact 

 dimensions of the lake. This is because of two 

 facts, firstly because its size increases greatly in 

 the wet season, secondly because it has not at any time of the year what 

 may be called a soHd margin, for it is completely surrounded by floating 

 islands formed by the growth and decay of vegetation. These islands, 

 which are massed together round the edge of the lake, are one of its 

 most characteristic features. Many different kinds of plants take part 

 in their formation, but those of primary importance are certain large 

 grasses and sedges that send out long floating runners from which new 

 upright stems arise. Floating plants such as duckweed become en- 

 tangled amongst these runners, and at the same time submerged weeds, 

 especially a species of Geratophyllum, grow up to the surface, where their 

 upper parts are killed by the heat of the sun or the growth of algae. 

 The mass of vegetation thus entangled is further agglutinated by the 

 luxuriant growth of an alga belonging to the family Rivulariaceae 

 which forms large brownish masses. These elements of the island in 

 the making both decay and grow. Their decay forms a kind of fen-peat, 

 which is prevented from sinking by their floating and growing parts. 



A floating island covered with rich soil is thus formed, and plants^ 

 of a great variety of species grow up upon it, forming dense entangled 

 masses. Even conspicuously flowering orchids and 

 oa mg sans. small shrubs flourish in a little time. These islands 



not only afford shelter and food for a large part of the fauna, but are of 

 great importance in practical agriculture. When a cultivator wishes to 

 grow tomatoes, cucumbers, or indeed any kind of vegetable, he. cuts off a 

 piece of a floating island sufficiently large to form his field, and then ties 

 a rope to it and tows it to a suitable situation. The next operation is to 

 turn the island upside down, which is easily achieved as its equihbrium 

 is by no means stable, to anchor it with a bamboo pole thrust through 

 it into the bottom of the lake and then to pile up more peat from the 

 bottom upon the exposed surface until it becomes soHd enough for him 

 to walk upon, and even to build a house or erect a pig-sty. The 

 gardens thus formed are extremely fertile. 



The presence of the floating islands, cultivated or in their natural 

 state, causes a very distinct differentiation of the lake into two regions, 

 an open central region and a swampy marginal zono. As we shall see, 

 the fauna of these two regions is very distinct. I have also been able to 

 recognize an intermediate zone, where the two regions meet. 



At the ends of the lake,' and especially at the southern end (to which 

 floating matter is carried by a quite perceptible current), a considerable 

 area is covered v,'ith floating islands, merging gradually into swampy land. 



The bottom of the marginal zone, beneath the islands, is com- 

 posed very largely of a black peaty substance somewhat inimical 



to animal hfe. That of the central region is 

 Nature of the bottom. ^ r , Qi. • ^-^ i- 



of a very peculiar nature, btrictly speaking, 



indeed, the lake has not a solid bottom at all. Beneath the water 



there is a layer of semi-liquid consistency composed of extremely 



1 Large botanical collections were made and have b3en deposited in the herbarium 

 of the Botanical Survey of India. 



