REVIEWS 633 



tected soil varied more in the course of a year than in the protected 

 soil. After prolonged drouth the ground water in both forest soil and 

 open soil may be the same but the moisture content of the superficial 

 layers is greater in forest soil than in open soils. This is due to the 

 fact that in forest soils the loss of water from the surface is being 

 replaced by ground water, while in open soils no such reservoir exists. 



The stream of the Rappengraben watershed carried more deposit 

 than the stream from the forested watershed. This deposit came from 

 landslides and from erosion in the gullies. No avalanches of sand or 

 stone occurred during the time of observation in the forested water- 

 shed, while they did occur in the partially forested watershed. 



Such in brief are the deductions made on the basis of many years 

 of careful measurement and observations of one forested and another 

 unforested watershed. R. Z. 



Groiuth and Form of Trees. Tropismen und exzentrisches Dicken- 

 wachstum der Baume. Ein Beitrag zur Physiologic und Morphologic 

 der Holzgewachse. Engler, Arnold. Schr. Stift. Schnyder von 

 Wartensee, Zurich. 31 :1-106, Figs. 1-30, Tables 1-43, 1918. 



Nouvelles recherches sur I'accroissement en epaisseur des abres. 

 Eassai d'une theorie physiologique de leur croissance concentrique et 

 excentrique. Jaccard, Paul. Pub. Foundation Schnyder von Warten- 

 see, Zurich. 23:1-XIII, 1-200, Pis 1-32, Figs. l-17o, Tables 1-23, 1919. 



The Schnyder von Wartensee prize essays afford an interesting side- 

 light upon Swiss neutrality during the late war. In 1913 the War- 

 tensee Foundation opened a competition of three years duration to 

 stimulate new 'investigations upon the growth in thickness of trees. 

 First prizes subsequently were awarded to Arnold Engler for an essay 

 in German, and to Paul Jaccard for a memoir in French. 



Engler concerns himself with the effects of geotropic and heliotropic 

 stimuli upon the growth, structure, and form of conifers and dicotyle- 

 dons. Fie reaches the striking conclusion that stout, rigid stems — 

 as well as young, flexible shoots — of dicotyls may develop marked 

 geotropic and heliotropic curvatures, but holds that in conifers, helio- 

 tropic bending is confined to the younger and more pliable portions of 

 the stem. As evidence in favor of these views Engler cites the crooked 

 or curved stems of trees growing under peculiar environmental condi- 

 tions, that is, on steep slopes, displaced from the normal, vertical posi- 

 tion, in unilateral illumination, etc. He considers that on steep slopes 



