50 COMMUNITY FUNCTIONS— DYNAMICS OF BIOTIC FORMATION 



Each of these types is subdivided as is item 3, as illustrated in 

 Figs. 4 and 5. 



The biologist who wishes to pursue this subject further is referred 

 to Tansley and Chipp (1926) and to the comprehensive monograph on 

 life forms of flowering plants by Du Rietz (1931). 



Biotic System of Life Forms. Gams has proposed a classification 

 that includes both plants and animals, as an outcome of recognizing 

 the importance of the biotic community (1918). The major bases 

 employed are substratum, motility, nutrition, and duration, and the 

 primary divisions are: (1) the adnate form, Ephaptomenon; (2) the 

 radicant form, Rhizumenon; and (3) the errant form, Planomenon. 

 The difficulties of a combined system are seen in the fact that the 

 radicant form consists exclusively of plants, whereas the other two 

 groups are composed chiefly of animals. Nevertheless, this first essay 

 contains much that is suggestive and may w^ell serve as a basis for 

 future development. 



Marine Life Forms. In his study of the communities of Gullmar 

 Fjord, Gislen (1930, a, h) , has proposed a system of marine bcnthonic 

 plants and animals, the main features of which are as follows: 



1. Crustida: (1) eucrustida, incrusting forms; (2) torida, cushion form; (3) 

 mammida, wart form; (4) digitida, finger form. 



2. Corallida: (1) dendrida, slirub form; (2) phyllida, leaf form; (3) umbracu- 

 lida, umbrella form; (4) umbellula form; (5) plume form; (6) rod form; 

 (7) fan form. 



3. Silvida: (1) graminida, grass form; (2) foliida, leaf form; (3) sac form; 

 (4) palm form; (5) buoy form; (6) whip form; (7) shrub form; (8) sar- 

 gassus form; (9) radial form. 



4. Radiida, radiate form. 



5. Valvida, bivalve form. 



6. Conchida, snail form. 



7. Limacida, slug form. 



8. Vermida, worm form. 



9. Crustaceida, crustacean form, 

 10. Piscida, fish form. 



The advantages in the use of such terms are not very evident. 



Sessile Multiple-individual Animals. Among plants, life forms 

 have proved very useful in designating and characterizing communi- 

 ties. This is due to the fact that they have segregated themselves 

 into climatic groups that give the essential character to grassland, 

 tundra, desert, deciduous forest, coniferous forest, etc. It is impor- 

 tant to emphasize the fact that plant ecologists are led to expect 

 similar conditions in animal communities in general, and usually 



