48 COMMUNITY FUNCTIONS— DYNAMICS OF BIOTIC FORMATION 



relations to the weather ordinate; the period before lambing is im- 

 portant to the females, and that of birth and the few days or weeks 

 following are critical for the lambs. 



One feature of life histories in general is the occm'rence of dor- 

 mant or quiescent states remarkably well represented in the several 

 groups found in fresh water and on land. The spores and cysts of 

 protozoa, the gcmmules of sponges, the eggs of arthropods, the pupae 

 of insects, and the hibernating ground squirrel afford well-known 

 examples, and suspended development in the embryos of a few mam- 

 mals may be analogous. Such quiescent states have much seasonal 

 significance, and their relations need to be ascertained especially in 

 connection with community aspects. 



LIFE FORMS 



Concept and Significance. The concept of the life form came into 

 existence originally as a consequence of the interest of plant geog- 

 raphers in the physiognomy of vegetation. It led logically enough 

 to various systems of classification, usually with much in common, 

 but with the emphasis on different criteria. Some of these were con- 

 structed in great detail, others were more inclusive; in one case, vege- 

 tation was the major objective, in another, floristics. Practically all 

 were static rather than dynamic, and the inductive approach through 

 experiment was entirely neglected, in spite of the fact that life forms 

 afford striking opportunities for the study of adaptation. As a con- 

 sequence, classification became stereotyped with little direct applica- 

 tion to dynamic ecology, though the system of Raunkiaer, with the 

 related biologic spectrum, has been much employed in floristic ac- 

 counts. Nevertheless, life forms do epitomize the adaptation of the 

 plant body under the compulsion of the environment, and hence are 

 of primary importance in connection with climax and succession. For 

 this purpose, however, it is essential to distinguish various categories, 

 based chiefly on the degree of modification and fixity (Clements, 

 1920:57; 1928:263). 



Kinds of Life Forms. Probably the most logical and serviceable 

 definition of the life form is that which includes under it all the 

 forms exhibited by plants and animals, such as taxonomic, vegetation 

 or biome, habitat, ecad, growth and competition forms (Clements, 

 loc cit.) . Among plants, the taxonomic and vegetation form are, for 

 the most part, identical in cryptogams; with flowering plants, this is 

 only exceptionally true. For the vast majority of animals, the 



