LIFE FORMS AND SYNECOLOGICAL UNITS 289 



The studies of Resvoll (1917) and of Nordhagen (1928) entirely con- 

 firm this conclusion. 



In the following classification of life forms, built on the frame- 

 work provided by Raunkiaer, and including cryptogams, eight main 

 classes are distinguished. The first three, comprising cryptogams 

 exclusively, are greatly in need of further elaboration. The other 

 classes have received more attention. Thus Raunkiaer's system, as 

 modified by Braun-Blanquet and others, takes the following form: 



I. PHYTOPLANKTON (mlcroscoplc floating plants): 



1. Areoplankton: microorganisms floating in air. 



2. Hydroplankton : microorganisms floating in water. 



3. Cryoplankton, protista inhabiting snow and ice, such as Sphaerella 

 nivalis, Scoiiella nivalis, S. antardica, and S. cryophila, which cause "red 

 snow"; and Ankistrodesmus nivalis, A. tatrae, and Stichococcus nivalis, 

 which cause "green snow" (see Chodat, 1896; Huber-Pestalozzi, 1925). 



II. PHYTOEDAPHON (microscopic soil flora): 



1. Aerophytobionts: aerobic soil flora (bacteria, etc.). 



2. Anaerophytobionts: anaerobic soil flora. 



III. ENDOPHYTES: 



1. Endolithophytes: lichens, algae, and fungi {Pharcidia lichenum) which 

 penetrate rocks. 



2. Endoxylophytes: parasites living in plants. 



3. Endozoophytes: protista living in animal organisms, often pathogens. 



IV. THEROPHYTES (annuals) : plants which complete their life cycle, from ger- 

 mination to ripe seeds, within a single vegetative period. Their seeds or spores 

 survive the unfavorable season under the substratum. Due to this habit and their 

 mobility they are widely distributed, even in the unfavorable hot, dry regions 

 of the earth. They include: 



1. Thallotherophytes: sUme molds (Myxomycetes) and molds with hetero- 

 trophic nutrition, also annual surface algae. 



2. Bryotherophytes: annual liverworts and leafy mosses such as Riccia, 

 Phascum, Ephemerum, and Physcotnitrium. 



3. Pteridotherophytes: annual vascular cryptogams with summer resting 

 period like Gymnogramme and Selaginella. 



4. Eutherophytes: annual seed plants including: 



a. Creeping therophytes Uke Tribulus terrestris and species of Amaranthus. 



b. Climbing therophytes like Vicia, Lathyrus, and Convolvulus. 



c. Erect therophytes like Linum and Aira. In cool countries this last is 

 almost the only group represented. 



Biennials which develop a leaf rosette in the first year and flowers the second 

 are to be classed with the hemicryptophytes. For the development of 

 eutherophytes the desert and steppe regions of the warm-temperate zone are 

 particularly favorable, i.e , where the competition of perennials is Umited. In 

 the cool-temperate and cold zones they are mostly restricted to cultivated areas, 

 where steppe conditions are artificially produced by man. 



