Grossenbacher Radial Growth in Trees. 9 



branches had a layer of tracheids not to exceed five or six while 

 a branch from which all dwarf-branches or assimilating leaves 

 had been removed on March 8 but on which the terminal buds 

 had been left, had developed a layer of eighteen to twenty 

 tracheids. 



In another experiment Jost removed buds from branches in 

 early May. When examined in fall it was found that at a cer- 

 tain point or line in the year's growth the radial diameter of the 

 tracheids was suddenly reduced and then increased again, thus 

 indicating the time when the buds were removed. The doubl- 

 ing effect on the wood ring resulting from the removal of the 

 leaves at a certain time, has since been investigated by Kuhne as 

 noted below. 



In a later paper Jost 21 reports some further experiments along 

 this line. Defoliated pine branches were found to undergo nor- 

 mal radial growth provided the terminal buds are not removed, 

 though they may be kept in the dark; while when the last 

 grown leaves and the terminal buds were removed very little or 

 no radial growth occurred. Practically the same results were 

 obtained following a similar experiment with Rhododendron. 

 Holes were bored into the trunks of various trees in late Sep- 

 tember and covered to prevent evaporation. By mid-October 

 callus formation had occurred in all but Tilia, even though gen- 

 eral growth had ceased. That is, it appears that although 

 cambial activity is usually started by leaf or shoot elongation 

 wounding may also induce it, and that not the availability of 

 food but a distal connection with some growing leaf-structures or 

 buds is necessary for the occurrence of radial growth. This 

 same phenomenon is also indicated by the results of an experi- 

 ment with Periploca. Although this plant has bicollateral 

 bundles, removing a girdle of bark prevented radial growth on 

 the basad side of the girdle. Nordlinger 22 had noted that in 

 case of most trees from which the branches are removed in win- 

 ter practically no radial growth occurred during the following 

 vegetative season although in some instances slight growth re- 

 sulted- 



J1 Jost, L. Ueber Beziehungen zwischen der Blattentwicklung und 

 der Gefassbildune: in der Fflanze. Bot. Zeit. 51:89-138. 1893. 



^Nordinger, H. Der Holzring als Grundlage des Baumkorpers. 

 Stuttgart. 1871. pp. 47. 



"Vochting, H. Zur experimentellen Anatomie. Nachrichten Kgl. 

 Ges. Wiss. Gottingen. 1902:278-83. 1902. 



