JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.When we speak today of ecological environments we usually think of extensive geographic or formational units. This is a very natural attitude in a comparatively new field, such as ecology, where many of the broader aspects of the science are still almost unexplored. At the same time we cannot escape the realization that each of the larger ecological units is composed of many smaller units, and that it is only by the detailed study of these smaller parts that we can ultimately come to a full understanding of the complex factors comprising the more extensive associations.In many instances these small units are ecological entities as distinct from one another as the association of which they are a part is different from other associations. This paper is a discussion of one of these smaller ecological units, the felled tree trunk.The fauna and flora comprising the living population of a log is distinctly characteristic of this environment. The living things that find in the log food, shelter, and opportunity for the reproduction of their kind are as well adapted for the specific conditions in which they live as are those organisms that live in any other environment. Furthermore, there is a definite succession of organisms as the chemical and physical character of the wood changes during the process of disintegration and decay. There is a regular progression from truly wood eating (xylophagous) forms toward an association of organisms characteristic of the duff strata of forest soils. In a brief paper of this character it is impossible to cover adequately this complete ecological succession, so we shall confine ourselves here to a discussion of the primary or xylophagous stage. In this stage of succession insects and fungi hold the center of the stage with the other organisms playing a minor r6le, whereas in the last stages of decomposition the bacteria are probably of major importance.The primary organisms of the xylophagous stage are those that are able to digest and assimilate the food materials available in the freshly cut log. These forms intergrade imperceptibly into the second stage of the succession which is composed of organisms that cannot convert sound wood into living protoplasm, but are dependent upon the primary forms to modify the food material in such a manner that it becomes available. Thus without the xylophagous organisms the food materials within the log would remain securely 26 397 This content downloaded from 128.235.251.160 on Sun, Ecology, Vol. VI, No. 4locked up, and the development of the succeeding stages would be impossible. One of the important fact...

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The subject of this paper was selected with enthusiasm. The law of natural compensations seemed most intriguing and the part played by forest insects in its enforcement appeared to afford unusual opportunity for discussion. Now that the time has arrived for its presentation there is a sense of trepidation, because the drawing of generalizations is always dangerous. However, without generalizations we should inevitably be confused by the mass of information concerning populations of insects, their parasites, predators, and host plants, and the responses of these organisms to their habitat. Therefore, it may be appropriate to present this somewhat old story from a different angle to illustrate the viewpoint of one forest entomologist, using some old and some hitherto unreported examples. Most of the examples that will be cited, whether old or new, have been observed first hand.