10 New Yoek State 



dependent upon the action of the current for transport. Further- 

 more, while the naturalist may at times collect a few specimens for 

 study, the abundance of the forms is, generally speaking, so great 

 that the effect of such collecting cannot be detected immediately 

 after it has been done, and in most cases the only way in which this 

 fauna and flora can be eliminated is through the influence of unfavor- 

 able conditions in the environment. If some chance fisherman has 

 hunted certain kinds of insect larvae for bait, such as dobson and 

 helgramites, there are still to be found normally scores and hundreds 

 of other sorts, and their absence is clear evidence of some general 

 influence of an unfavorable character. Furthermore, the argument 

 does not rest upon any particular species or even upon any single 

 group and takes into account both animals and plants, the kinds 

 that grow fast to the stones on the bottom, those that frequent 

 shallows, or occur only in the deeper places, the varieties that float 

 in the water as well as those that burrow in the bed of the stream. 

 Finally, we know in considerable measure the relation of individual 

 organisms to water conditions. We recognize that certain species 

 are rare and others abundant, that a given form occurs only in pure 

 waters and other types are seen only in polluted streams. We 

 recognize also types that are intermediate and so by the gradual 

 appearance and disappearance of series of organisms we can trace 

 directly the transition from an area of pure water with its character- 

 istic organisms to a polluted region with entirely different types of 

 life, or in the extreme instance, without any living organisms what- 

 ever 



The estimate which one places on biological conditions of the 

 land surface in any given region is based, not upon a single item but 

 upon the general appearance of the area, and takes into account all 

 of the features. We have come in daily contact with these so long 

 that we take in complex factors at a glance and pass judgment 

 almost instantaneously with regard to the condition of the lawn, or 

 field, or garden tract. Now, the same test may be applied without 

 difficulty to water bodies, though it is, for reasons already mentioned, 

 not quite so easy to see the condition as in the case of a land area. 

 We observe the sum total of appearances along the shore, in shallow 

 waters, on bars in the stream, over the bed of the river or lake, 

 and even in the open water itself. To be sure one is dealing here 

 with factors which are not familiar to the ordinary individual, but 

 they are well known to the students of such areas and data are easily 

 accessible to the individual who desires to inform himself with re- 

 gard to the situation. 



