Periodical Literature. 449 



ing on the rate of growth. Other species investigated in these 

 directions were beech, oak, and Norway Spruce. Regarding the 

 latter it was found that the influence on the cross-section incre- 

 ment was not as large as in the Douglas Fir. Here, also, the de- 

 crease in height growth of twelve-year-old spruces was noted, but, 

 after a few years, the height growth again gradually increased. 



When removing one-third of the crown in August, 1905, the 

 progress of the height growth for the different years was 



When removing one-half of the crown the progress was 

 31 17 24 14 31 54 cm. 



When only dry branches were removed, 



46 21 19 47 45 60 cm. 



Untersuchungen iiber die Auf ashing der Waldb'dume. Centralblatt 

 f. d. g. Forstwesen. October, 1909. Pp. 413-427. 



Dr. Metzger, who some fifteen years ago 

 Mechanics advanced most interesting theories to ex- 



of plain the laws of mechanics under which 



Tree Growth. the form of tree trunks is built up, publishes 

 similar investigations of the static and me- 

 chanical principles involved in the minute anatomy of the wood. 

 The discussion, the author admits, lacks experimental basis, and 

 is therefore fragmentary. 



The author discusses the problem of epi- and hyponasty. Why 

 in conifers the underside of branches, in deciduous trees more 

 often the upper side shows increased tissue formation, is one of 

 them. That these tissues are mechanical adaptations to give in 

 one case additional compression strength, in the other additional 

 tension strength, seems clear. The tension strength of the upper 

 side of a birch branch showed nearly double that of the lower 

 side. 



The author finds altogether, that deciduous trees are constructed 

 more for tension, coniferous trees more for compression, although 

 some data appear to contradict this finding. In wind breakages, 

 with conifers the broken stem usually preserves connection with 

 the stump on the leeward, i. e., the compression side, while in 



