APPENDIX 525 



3. Supplementary Studies 

 PLANCTON. 



A supplementary study in adjustment (to follow p. 369). 



In all lakes, ponds and streams there exists a population of 

 microscopic plants and animals suspended in the open water, 

 or floating or drifting or swimming about, collectively known 

 as plancton. It is a vast assemblage of minute, transparent 

 organisms, the existence of which was not suspected a hun- 

 dred years ago. Being invisible they were unnoticed. Yet 

 they constitute a vast population, well adjusted to its place 

 in the world, self-sufficient, self -maintaining, and independent 

 of the life of the land. Both plant and animal forms show 

 many adaptations to a life of drifting about in the open 

 waters. Their very minuteness greatly favors drifting, but 

 in addition to this they secrete internally bubbles of gas or 

 drops of oil, lightening their specific gravity, or they develop 

 long hairs and spines which greatly increase superficial area, 

 and surface friction with the water. 



Plancton organisms include of necessity many chlorophyl 

 bearing forms, (green, or blue-green or light amber-brown in 

 color) : these constitute the producing class. Animal 

 forms are present also in great variety, and constitute, as on 

 land, the chief consuming class. The following groups are 

 commonly found in the plancton : 



ALGAE Diatoms (see fig. 49 on p. 67.) 



Desmids (see fig. 42 on p. 56 ; fig. 46,7, g and h, on p. 



65; fig- 50 on p. 68.) 

 Flagellates (see fig. 6 1 on p. 105 ; fig. 62 and 63 on p. 



106; fig. 64 on p. 107 and fig. 65 on p. 108.) 

 Other algae (see fig. 44 on p. 60; fig. 46, a, 6, c, and d 



and fig. 47 on p. 65; fig. 187 on p. 334.) 

 PROTOZOA (see fig. 51 on p. 70; fig. 53 on p. 76; fig. 257 on 

 P- 439-) 



