1020 The American Naturalist. [December, 
If we consider the ponds with reference to the growths of or- 
ganisms, we obtain from the above table the following sum- 
mary: 
TABLE No. 5. 
Number of Ponds and Reservoirs 
Group Number per c. e. j 
Diato- Chloro- | Cyano= F ‘7, fusoria. 
mace. phycee. | phyceæ. | y 
| | 
BEN TED 7h, O VEBE a Baca Mh : aioe i | — -| = 
I Often above 1000 per c. c. 24 5 | 7 | 8 
II Occasionally above 1000 per c. c. 8 11 | 10 | 7 
III | Usually between 100 & 500 per c. c. 19 29 18 | 35 
IV | Below 100 perc. c. 6 12 | 22 | 
From this it appears that the Diatomaceæ are the organisms 
most commonly found in large numbers. There are 24 ponds 
(42 per cent of the ponds considered) which often have these 
organisms as high as 1000 per c. c., while in only 6 (11 per 
cent) are they always below 100 per c. c. The Chlorophyceæ 
are not often found in great abundance, though many ponds 
contain them in moderate numbers. Only 5 ponds (9 per 
cent) have growths of 1000 per c. c., while 29 (70 per cent) 
have growths of from 100 to 500 per c. c. The Cyanophyceæ 
are notas common as the Chlorophyceæ, but where they do 
occur their growth is usually greater and they cause more 
trouble. There are 7 ponds (12 per cent) that commonly 
have growths above 1000 per c. c., while in 22 (39 per cent) 
they are never above 100 per c.c. The Infusoria are some- 
what more abundant than either the Chlorophyceæ or Cyano- 
phyceæ. 8 ponds (12 per cent) often have growths above 1000 
per c. c.; 35 ponds (60 per cent) have growths between 100 
and 500 per c. c. 
From Table 4 it also appears that 28 ponds (49 per cent) 
often have high growths of one or more of these classes of or- 
ganisms at one time or another during the year. Such 
growths, except in the case of certain diatoms, are almost 
always noticeable and frequently are very troublesome. In 
seventeen ponds the Diatomacez alone reach 1000 per c. ©; 
in one pond the Cyanophycee alone; and in three ponds the 
Infusoria alone. One pond has high growths of Diatomace®, 
