Grossenbacher — Radial Growth in Trees. 37 



deprived of marked radial as well as elongation growth for sev- 

 eral years, and the long-continued scarcity of food in the upper 

 part of the top is said often to result in the dying back of the 

 upper branches and thus gives rise to stag-horn effects. The 

 length of time required for adjustment to the new environment 

 is said to depend upon the extent of a tree 's leaf surface. The 

 sprouts, which often arise on long bare trunks, are thought to 

 be induced by the swaying action of the wind thus tending to 

 develop a lower head. 



An enormous amount of data and calculations on the relation 

 of the environment to radial growth and its distribution was also 

 calleeted by Schwarz 71 and published as a monograph which in 

 addition contains many very important observations on the life 

 and seasonal history of Pinus silvestris. It is noted that yearly 

 radial growth as measured by the area of its cross section in- 

 creases in trees until the age of about 20 to 30 years is reached, 

 but under very favorable environmental conditions its growth 

 may increase to the age of 100 years. His general conclusions 

 regarding the wind in its relation to the distribution of radial 

 growth are practically the same as those put forth by Schwen- 

 dener and Metzger. Some instances are cited where the tops of 

 t^ees had been broken off when about 30 years old and which had 

 since grown about 60 years with lateral branches diverted to 

 function as the main axis. In the region of curvature of the 

 branch which assumed the functions of the main axis excentric- 

 ity became very marked, with the greater radius on the under 

 side. It is thought that the excessive pressure or welgnt on the 

 under side was the stimulus to increased radial growth on that 

 side. In one case, in which the curvature induced had been such 

 as to exert the greater pressure on the upper side in one place, 

 it was found that this upper side had the greater radius. Many 

 measurements on vertical stems also showed a greater radius on 

 the leeward side in regard to the prevailing wind. By tying a 

 young pine tree in a bent position excessive growth resulted on 

 the compressed side, i. e. it seems that a fixed, bent position ex- 

 erts the same influences on radial growth as the discontinuous 

 pressure due to wind swaying. Other measurements on slightly 

 inclined trees also showed a greater radius on the side toward 

 which the trees inclined. It is held that relative amounts of 



71 1. c. 



