40 COMMUNITY FUNCTIONS— DYNAMICS OF BIOTIC FORMATION 



erect, aggregation is favored and migration is slight or absent. Dura- 

 tion is partly a matter of life form and partly of the type and amount 

 of growth, as is shown by the varied behavior of the species of Erythro- 

 nium. The kind and degree of competition are modified by the rela- 

 tion between aggregation and migration, competition between individ- 

 uals of one species being emphasized in the one instance and between 

 two or more species in the other. For the details of life histories from 

 the morphological standpoint, "Die Lebensgescliichte dcr Bliitenpflan- 

 zen Europas" is a mine of information (Kirchner, Loew and Schroter) ; 

 from the ecological point of view, the life cycle has received atten- 

 tion on an experimental basis (Clements, AVeaver, and Hanson, 1929). 



Reproduction. By contrast with the preceding processes, sexual 

 multiplication or reproduction is concerned with the flower and its 

 products, fruit and seed. In essence, however, it is but a continuation 

 of the growth of the individual, and the seed is in effect the analogue 

 of the bud. Since the flower is not a food-making organ, it is less 

 intimately related to the habitat than the shoot, though its periodic 

 behavior, both as to season and day, is directly connected with tem- 

 perature, and to a smaller degree with water and light. A number of 

 flowers exhibit a definite cycle of opening and closing, and related 

 movements not infrequently occur in the flower cluster as well. 



The behavior of a flower is determined in large measure by its 

 structure, which is a matter of its phyletic position or taxonomic 

 form. This controls the type of flower cluster and the kind and ar- 

 rangement of the flowers, and in consequence the major phases of the 

 reproduction cycle, namely, blooming, pollination, fruiting, seed pro- 

 duction, and dissemination. In the present instance, the limitations 

 of space permit only the most concise treatment of these, and to 

 obtain a basis for detailed studies in this field it is necessary to turn 

 to the comprehensive accounts of the several processes. As before, the 

 "Lebensgeschichte" is invaluable for this purpose, while for blooming 

 and pollination, Knuth's "Handbook of Flower Pollination" is of par- 

 ticular importance. The experimental approach, especially from the 

 ecological standpoint, is embodied in "Experimental Pollination" 

 (Clements and Long, 1923), and "Anthokinctics" (Goldsmith and 

 Hafenrichter, 1932). 



Structure of Flower and Cluster. The life cycle of a flower is 

 dependent upon its structure; the manner of pollination is connected 

 with both structure and arrangement. The daily round of floral be- 

 havior is wrought upon the pattern supplied by the number, position, 

 and structure of the four parts, calyx, corolla, stamens, and pistil. 

 It is intimately connected with the task of securing the proper trans- 



