PERIODICAL LITERATURE 331 



'effects. Raunkiaer has shown the utihty of such a scheme by analyz- 

 ing several European evergreen shrub formations. He states that his 

 leaf size classes are not the only quantitative units to be employed, 

 but proves their adaptability to statistical methods. 



Raunkiaer's valence method offers a good means of studying a for- 

 mation by differentiating its species according to their frequency ex- 

 pressed numerically, which serves both as a means of comparing closely 

 related formations and also as a basis for an ecological comparison. The 

 frequency is determined by taking a number of sample plots of a certain 

 :size and expressing numerically for each species the percentage of 

 plots on which it occurs. The necessary number of plots is obtained 

 as soon as the result becomes practically unchanged with the addition 

 of more plots. Raunkiaer found that o.i sq. mm. was a suitable size, 

 and gave fairly constant results with from 25 to 50 plots. 



All who are interested in the details of the methods and unable to 

 read Danish should consult the English papers cited. The latter trans- 

 lation is concluded with the following paragraphs, which speak for the 

 merits and utility of these statistical methods in ecological work with 

 vegetation, including forest investigations : 



"The above is a system of formation analysis into primary divisions so funda- 

 mental that the biological and physiognomical coincide and are both emphasized. 

 Within its limits there is a place for offshoots, or subdivisions of larger or 

 smaller extent, expressing characters of special biological significance which re- 

 quire special biological (ecological) characterization in the systematic analysis 

 of a narrowly limited formation. 



"By more intensive studies of climatic factors, of soil chemistry, of physical 

 and biological conditions, and by a wide investigation of the morphological, ana- 

 tomical, and physiological nature of plant species, ecology will be able to reach 

 .an understanding of the place of each individual species in a formation." 



C. F. K. 



SOIL, WATER, AND CLIMATE 



In studying the effect of the precipitation factor 

 Redwood in limiting the distribution of the redwood i,Sc- 



Distrihution qiioia scrnpervirens) in California, William v^. 



in California Redwoods Cooper secured measurements of pre- 

 cipitation at 22 stations in the Santa Cruz Moun- 

 tains and in the Santa Clara Valley. Certain areas, not differing ma- 

 terially in topography and soil from adjacent areas supporting luxuriant 

 redwood forests, are practically treeless, except for scattering speci- 

 mens of Quercus agrifolia and Q. lobata. He shows that heavy winter 

 rainfall is necessary for the development of the redwood forest. The 



