No. 1, July, 1920) ECOLOGY, PLANT GEOGRAPHY 45 



300. Polk Evans, I. B. The plant geography of South Africa. Official Year Hook Qnion 

 of South Africa 2:. r )l 58. 1919, — This is a reprint of the paper in the Year Book for 1918 

 [See Bot. Absts. 1, Entry 468.] 



301. Raunki a Kit, C. Recherches statlstiques sur les formations vege tales. [Statistical 

 Investigations on plant formations.] Kgl. Dansk. Vidensk. Selskab. Biol. Meddel. I;. 80 p. 



3 fig. 25 tables. 1918. — Theaut lior has here summarized the material of his former contributions 

 and shown something of their applications to the solution of problems of ecological plant 

 geography. I lis statistical or valence method consists in analyzing a plant population by 

 means of the scrutiny of certain unit areas of 0.1 sq. m. outlined by a metal radius of suit- 

 able length attached to a walking stick. From the examination of 25 to 50 such areas the 

 frequency with which a given species occurs is determined and is expressed as a frequency 

 percentage, frequency coefficient or valence. He defines his "formation" as a plant com- 

 munity that is homogeneous from a floristic point of view with respect to the species show- 

 ing the highest frequency coefficients. In areas that have been relatively undisturbed he 

 believes that an equilibrium will be reached and he formulates a law relative to the occur- 

 rence of species within such a community. "In a formation in a state of equilibrium one or 

 more species will prosper at the expense of their neighbors because such dominant species are 

 better adapted to live under the conditions existing within the formation of which they are 

 a part, and by their aggregation they will prevent other species from equalling them in fre- 

 quency. But however well they may be equipped for such community life they cannot pre- 

 vent other species, widely disseminated but fewer in individuals, from entering the forma- 

 tion and there occupying portions that for any reason may have been left bare of the domi- 

 nant species. It follows that there is a much larger number of the less frequent species." — 

 A similar method for determining the relative area occupied by each species is described and 

 a classification of vegetation on the basis of life-forms and leaf-sizes given. [See also Bot. 

 Absts. 4, Entry 198. Also Jour. Roy. Microsc. Soc. 1919:52-53. Also Nature 103: 33. 

 Also rev. by Moreau, Bull. Soc. Bot. France 66: 58-59.] — Geo. D . Fuller. 



302. Schroder, Bruno. Die Vegetationsverhaltnisse der Schwebepflanzen in Schla- 

 wasee [Silesia]. [Vegetational relations of the plankton of the Schlava Lake.] Ber. Deutsch. 

 Bot. Ges. 36: 648-659. 2 jig. 1918. — A seasonal study of the plankton shows that the great- 

 est number of species is found during the summer, the smallest number, a little more than 

 one-third, during the winter season. The schizophytes, chlorophytes and phaeophytes 

 appear throughout the year, the conjugatae primarily during the summer. Cladothrix is 

 present the year around. Temporary variations are observed. In the case of Ceratium 

 hirundinella, however, the individuals remain unaltered as regards form and size. — Ernst 

 Artschwager. 



303. Shreve, Forrest. Vegetation of southern South America. [Rev. of: Skottsbero, 

 Carl. Botanische Ergebnlsse der swedischen Expedition nach Patagonien und dem Feuer 

 lande 1Q07-1909. V. Die Vegetations-verh'altnisse l'angs der Cordillera de los Andes S. von 

 41° S. br. [Botanical results of Swedish Expedition to Patagonia and Tierra del Fuego, 1907- 

 1909.— V. Vegetation of the Andes south of 41° south latitude.] Kungl. Svensk. Vet. Handl. 

 56:1-366. PI. 23. 1916.] Plant World 22 : 55-56. 1919. 



304. Sim, T. R. Soil erosion and conservation. South African Jour. Indust. 2 : 715-724. 

 1919. — Vegetation is a preservative covering. It is protective against insolation, drought, 

 radiation, wind, flood, and donga formation. The vegetation has an effect on the atmosphere 

 and conversely the atmosphere has an effect on the vegetation. Concentration of water 

 should always be prevented, if possible, but in the lower grades of plant succession, especially 

 w r here close turf and humus are absent, such concentration is exceedingly dangerous and 

 leads directly to all serious cases of donga formation, erosion of cultivated land and river 

 erosion. — E. P. Phillips. 



