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 dost 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 Kiihne as 
noted below. 
In a later paper dost 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 w T ere removed very little or 
no radial growth occurred. Practically the same results were 
obtained following a similar experiment with Rhododendron. 
Holes w r ere 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- 
21 Jost, L. IJeber Beziehungen zwischen der Blattentwicklung und 
der Gefassbildung in der Pflanze. Bot. Zeit. 51:89-138. 1893. 
22 Nordinger, H. Der Holzring als Grundlage des Baumkorpers. 
Stuttgart. 1871. pp. 47. 
23 Vochting, H. Zur experimentellen Anatomie. Nachrichten Kgl. 
Ges. Wiss. Gottingen. 1902:278-83. 1902. 
