Grossenbacher — Radial Growth in Trees. 43 



actual needs. On the other hand from the work of both Jost 

 and Lutz it is also evident that the presence of food, transpira- 

 tion current and suitable environment alone do not result in 

 radial growth when no developing buds or shoots are present; 

 i. e., cambial activity seems somehow to be dependent upon 

 elongation growth or some enzyme activated or produced by it. 

 The determinations by Fabricius, however, have made it ap- 

 parent that the distribution of reserve food in tree-trunks seems 

 to be in accordance with some unknown law, which brings about 

 maxima and minima of food storage in more or less definitely 

 alternating regions. The marked differences in the amounts of 

 reserve food in the regions of maxima and minima could not be 

 attributed to differences in the storage capacity of the regions 

 for such differences would have been noted, nor to the distribu- 

 tion of the branches because the wave-like succession of maxima 

 and minima also occurred and it was usually most marked on 

 the branchless portion of trunks. There is some indirect evi- 

 dence to be had from the cited papers which tends to show that 

 the places of the inception and longest duration of radial growth __ 

 in a general way are the places of maximum food storage, "and 

 therefore gives support to Mer's 86 contention to the effect that 

 radial growth begins first where most food is stored and is most 

 active and persists longest in such regions. The Schwendener- 

 Metzger-Schwarz hypothesis suggests another way out of the 

 difficulty by its assumption that wind action is responsible for 

 the distribution of both metabolized food anti. radial growth. 

 But we cannot admit the far-reaching claim of these investiga- 

 tors that wind and gravity are the only formative factors con- 

 cerned in the distribution of radial growth especially since light 

 and transpiration have been shown to be powerful formative 



agents. 



i 



OBSERVATIONS ON THE DISTRIBUTION OF LATE RADIAL GROWTH ON 



FRUIT TREES. 



While studying crown-rot of fruit trees during a series of 

 years, I found that the initial bark injuries which afterwards 

 result in the disease usually occurred in places at the base of 



80 Mer, H. Sur les causes de variation de la densite' des bois. Bui. 

 Soc. Bot. France. 39: 95-105. 1892. 



