2i6 Forestry Quarterly. 



cause of the treeless condition has been proven in many instances 

 in a most convincing manner. 



Furthermore, the minimum, amount of precipitation which is 

 necessary for the existence of the forest must vary with the 

 conditions of the soil, especially its moisture holding capacity. 

 It makes a great difference whether the moisture holding capacity 

 of the soil is 2 to 3 per cent, or 12 per cent. In case of sandy 

 soil with a very low moisture holding capacity (2 to 3 per cent.), 

 precipitation will penetrate deep into the ground and will become 

 available for forest growth, while in case of heavy, clayey soil 

 whose moisture holding capacity may be 12 per cent., with the 

 same amount of precipitation, water will remain in the upper 

 layer of the soil, from which it will rapidly evaporate without 

 becoming useful to vegetation. 



Unfortunately, Mayr did not state all the facts which lead him 

 to decide on his minimum amount of moisture necessary for the 

 existence of the forest. It seems doubtful that the amount of 

 precipitation during the four vegetative months is really the only 

 deciding factor in limiting forest growth. Tree distribution often 

 depends not so much on the amount of precipitation that falls 

 during the vegetative season as upon the amount of water ac- 

 cumulated in the soil during the winter and fall. 



Mayr's views on the mooted and complicated question of ac- 

 climatization, which is of such importance to the practitioner, as 

 well as to the theoretical man, are of interest. 



Mayr radically differs from the majority of foresters on the 

 question of acclimatization, on the ability of transmitting certain 

 characteristics acquired by trees grown under new climatic soil 

 conditions, and on the importance of the source of seed for for- 

 estation purposes. 



Mayr denies the possibility of acclimatizing or adapting a 

 species to new climatic conditions. He claims that each species 

 can exist only under certain climatic conditions. If it is intro- 

 duced into new environment in which it meets conditions to which 

 it was not accustomed in its native land it perishes. He further 

 claims that acclimatization of forest trees — if such exist at all — 

 requires such a long time that it has no practical value for man. 

 He also denies the possibility of hereditary transmission of va- 

 rious deviations from the mother type. He thinks that only the 

 typical characteristics are transmitted, but not the various de- 



