34 THE LIFE OF DEVILS LAKE 



This zone is characterized primarily, as its name implies, by 

 the Ruppia, which grows here abundantly, and secondarily by the 

 organisms which live attached to the Ruppia or to other organisms 

 which grow upon it. Chief of these is Cladophora, which forms 

 extensive masses and which, perhaps no less than Ruppia, is respon- 

 sible for the evolution of large quantities of oxygen in sunny 

 weather, and contributes an important amount of the bottom ooze 

 thru the decay of its filaments. The exact quantitative role which any 

 one of several organisms plays in a situation of this sort is a diffi- 

 cult one to determine and no attempt has been made to do so in 

 this case. It is, moreover, of minor importance since both organisms 

 exert a similar influence, the effect produced being a collective one. 



Growing on the Ruppia and Cladophora are numerous micro- 

 scopic forms, chief of which are sessile diatoms, peritrichous Pro- 

 tozoa and attached rotifers. There are many free-living forms also 

 which are numerous here and rare, or absent, elsewhere in the 

 lake. Chief among these are the Protozoa, rotifers, nematodes, and 

 mites, while a few others occur. 



The extent of zones 1 and 2 is naturally a variable one, depend- 

 ent on the slope of the lake bottom at different points. 



The pelagic zone, which comprises the major part of the lake, 

 has no forms peculiar to it, since all of its organisms occur in the 

 other two zones as well. It is characterized by the greater uni- 

 formity in the distribution of its inhabitants, tho great differences 

 occur here also, as will be seen later, and by the absence or rarity 

 of those forms which characterize zones 1 and 2. 



The bottom zone, which comprises the ooze on the lake floor, is 

 characterized positively by the presence of the larvae of Chirono- 

 mus, by nematodes and the rhizopod Arcella, and negatively by 

 the absence of pelagic species, tho some of the algae, especially 

 Coelosphaerium may occur there. This zone is frequently lacking 

 in oxygen, as has been mentioned previously, and will be discussed 

 later in connection with its inhabitants. 



PLANCTON METHODS AND RESULTS 



The determination of the distribution in time and space of its 

 inhabitants is the central problem in the investigation of any area, 

 for this problem involves the reaction between organisms and environ- 

 ment, and the adaptation of the former to the latter, which are the 

 essential questions of ecology. This determination is a matter of 

 considerable difficulty, for both land and water animals. Many 

 attempts have been made to devise satisfactory apparatus for 

 plancton collection, but thus far none has been invented which is 

 uniformly satisfactory for all kinds of organisms. Full discus- 

 sions of the advantages and disadvantages of various types ot 



