326 Forestry Quarterly 



this, however, is not at all as frequent as is usually supposed, and 

 more apparent, an ocular delusion, than actual. In desert plants, 

 and in others with small root system and hence reduced transpi- 

 ration, spring wood cells are thick-walled. According to Wieler, 

 this can be artificially produced by regulating water supply. The 

 same phenomenon was shown by the author in scrubby pines and 

 spruces from acid moor soils, which he explains as due to de- 

 ficiency of water reducing turgescence of tissues accompanied by 

 large amount of concentrated nutritive sap (osmotic pressure!), 

 which is used in thickening the walls. 



The phenomenon of double rings due to defoliation and of 

 change from spring to summer wood, and prevention of the vari- 

 ation due to regulation of supply of water and of food, enabling 

 King and Kiihns, Jost and Wieler to produce any desired forma- 

 tion, leaves no doubt that the anatomical variations in structure of 

 the wood accompany variations of water supply. 



As to the periodicity of growth phenomena and annual ring 

 formation, the usual explanation of hereditary habit is demolished 

 by the citation of most interesting observations of behavior in 

 tropical regions and experiments which show that exterior condi- 

 tions influence the periodicity and that some species have the 

 ability under given favorable conditions to grow uninterruptedly. 



Trees from the temperate zone, where periodicity of growth 

 coincides with periodicity of season, transplanted into tropical 

 conditions (Buitenzorg) show still periodicity, but vary this not 

 only from species to species, but from individual to individual. 



Nurserymen have learned to overcome the natural periodicity 

 by the application of ether vapor, warm water baths, water in- 

 jections below the buds, concentrated food supply, electric cur- 

 rent and intense light. Klebs' most interesting experiment with 

 a beech plant is cited, in which a beech still in foliage by Septem- 

 ber 11 was exposed to 200 candlepower light. After 10 days 

 the dormant buds began to lengthen and by September 25 a com- 

 plete new foliage was formed. After keeping it during October 

 to December in a hothouse, growing, by December 25 it was 

 exposed to a second illumination by 1,000 candlepower, and by 

 January 27 a third foliage was formed, complete by the middle 

 of February, the old leaves dropping. By the middle of March 

 a fourth foliage began to form naturally. 



