326 HENRY b. ward: 



Apstein (94) would divide lakes into two classes, plankton 

 rich and plankton poor, the first characterized by an abun- 

 dance of Clathrocystis and absence or rarity of Dinobryon, and 

 the second by reverse conditions. This classification is ques- 

 tioned Reighard (94), Zacharias (94) and Strodtmann (96) on 

 the basis of investigations in other lakes. The total amount 

 of plankton is believed by Steck (93) to depend on the length 

 of the shore line, and Reighard (94) also regards this as an im- 

 portant factor. Many observers have noted that there is in 

 general proportionally less in a larger than in a smaller lake, 

 and this has been found by Reighard (94a), Hofer (95), Walter 

 (95), Zacharias (95b;, Strodtmann (96) and others to be capable 

 of more precise statement in the principle that the amount of 

 plankton per cubic meter of water varies inversely as the depth. 

 Other factors affect the development of the plankton, chief 

 among them being light, (Stenroos, 98), transparency of the 

 water, (Steck, 93), and temperature, (Zschokke, 95). Walter 

 (95) emphasizes also the relation between the depth and the 

 area of the lake. 



In Norwegian hikes presenting a great variety of conditions 

 altitude, depth and rapidity of change in water contained 

 therein, lluitfelt-Kaas was able to show that shallow waters are 

 especially favorable for the development of the plankton while 

 deep basins are under otherwise like conditions notably poorer. 

 This is true only in summer and is probably controlled largely 

 by temperature conditions. Even more important, however, 

 is the drainage area of the lake and the proportionate inflow 

 and outflow, so that in basins with rapid change in water much 

 Less plankton is found than in more stable lakes. Here it is 

 evident that a shallow lake may be even less favorable for 

 the development of the plankton than a deeper one by virtue 

 of the greater instability associated with a limited volume. 



On the question of horizontal distribution Apstein (94), 

 bard (94a) and others have maintained the existence of uni- 

 formity. Zacharias was inclined to question this (94c, 94d) 

 but has since then changed his views (95c). In the case of re- 

 cent observers who have noted nonuniformity in distribution 



