330 JOURNAL 0I-' Fokl-STRY 



With the Northern Hemisphere, Raunkiaer recognizes three princi- 

 pal regional chmate-zones : 



(A) A tropical area with uniform and high temperatures, but a varying hu- 

 midity ; 



(B) To the northward an area of decreasing warmth correlated with an in- 

 creasing difference between summer and winter, but with a precipitation suitable 

 at most times for plant life; 



(C) Warmth decreasing from equator to pole, as in B, but with decreasing 

 precipitation, at least in summer. 



These climatic zones are characterized by biochores or plant-climate 

 boundaries. From this series three types of climate are suggested: (i) 

 phanerophytic, (2) hemicryptophytic, and (3) chamaephytic. 



To facilitate the comparison of different climates, Raunkiaer devised 

 "hydrothermic figures," by representing in a single diagram the curve 

 of the monthly averages of temperature and that of the monthly aver- 

 ages of rainfall ; then, by determining the biological types or combina- 

 tions of types corresponding with the hydrothermic figures, he obtained 

 the "biological expressions" of the various climates. These methods 

 are also applicable to altitudinal zones. 



Fuller and Bakke'^ have prepared somewhat abridged translations of 

 two of Raunkiaer's subsequent papers. Raunkiaer proposes another 

 quantitative method of much promise in the analysis of vegetation, 

 in so far as this unit is an expression of the biological value of a cli- 

 mate. He considers the size of the leaf as being physiologically impor- 

 tant, and, using the simple leaf as a standard, has suggested a system 

 of leaf classes. In his scheme there are six different classes: (i) 

 leptophyll, 25 sq. mm. ; (2) nanophyll, 9 x 25 sq. mm. =: 225 sq. mm. ; 

 (3) microphyll, 9" x 25 sq. mm. = 2,025 sq. mm. ; (4) mcsophyll, 9^ x 25 

 sq. mm. = 18,225 sq. mm. ; (5) macro phyll, 9* x 25 sq. mm. = 164,025 

 sq. mm. ; (6) megaphyll, limited only by the upper limit of macrophylls. 

 In order to facilitate the correct grouping of the leaves, the translators 

 have reproduced the graphic representation of the various limits of sur- 

 face area of the scheme. 



With this method Raunkiaer maintains that the biological factor for 

 climate, in so far as it influences leaf size, may be obtained. Compari- 

 sons may be made readily between two climates which have varying 



' Fuller, George D., and Bakke, A. L. : Raunkiaer's "Life Forms," leaf-size 

 classes and statistical methods. The Plant World, vol. 21, pp. 25-37, 57-63, Feb- 

 ruary and March, 1918. In review of: 



Raunkiaer, C. : Om Bladstrrelsens anvendelse i den biologiske Plant geografi. 

 Bot. Tidsk., vol. 33, pp. 225-240, 1916. 



Raunkiaer, C. : Om Valensmetoden. Bot. Tids., vol. 34, pp. 304, 311, 1917. 



