886 



Experiment Station at Geneva). No beneficial effects could be determined. 

 On the contrary, the plants were very evidently injured. Knobby dwellings 

 were formed on the axes; the leaves became sickly and the root system 

 less developed. 



A confirmation of my personal studies on the processes after girdling 

 may be found in Krieg's contributions on callus and wound wood formation 

 in girdled branches and their histological changes (Beitriige zur Kallus- und 

 Wundholzbildung gcringelter Zweige und deren histologische Veriinderun- 

 gen. Wiirzburg 1908, Nubers Verb). The observations on Vitis are new 

 in that the formation of new structures as a result of girdling were proved 

 in the pith, although the pith had not been injured at all. This fact is 

 important because it shows that the wound stimulus, or the changes in tissue 

 tension setting in after each injury, manifests itself in regions far distant 

 from the wound surface and separated from it by firm wood zones. This 

 makes better understandable the changes in the pith body due to frost 

 injuries in which the wood ring shows no disturbances of any kind. 



The formation of wound wood in the pith of Vitis was observed by 

 Krieg, who ascribes it to the action of the products of decomposition of the 

 woody part killed by the girdling. This wound wood consisted of parenchy- 

 matous aggregations resembling pith spots. These were enclosed by a ring 

 of cambium. The ring lying within the pith bark developed wood with 

 numerous vessels toward the inside and sieve tubes toward the outside. The 

 other pith spot, adjacent to the pith crown, formed the sieve tubes from its 

 cambial ring tdward the inside and wood toward the outside. The corre- 

 sponding parts of both new structures united later with the respective parts 

 of the overgrowth edge. In the meantime, the plant had replaced the wood 

 already killed in girdling by the formation of new wood and sieve tissue 

 in the pith. 



Page 825. W'e owe varied and careful experiments to Elsie Kupfer 

 (Studies in Plant Regeneration. Dissertation of Columbia University, New 

 York, 1907). Of these, we will emphasize first the experiments on root 

 cuttings of Roripa Armoracia. Pieces of the root laid flat in the soil formed 

 new shoots from the cambium of both the upper and under cut surfaces. If 

 bark and cambium had been cut away, sprouts developed after a preliminary 

 callus formation at different places near the vascular bundle and more 

 abundantly at the upper than on the under end. The capacity to form 

 sprouts, which otherwise is peculiar to the cambium, therefore, extends in 

 this case to the callus tissue newly produced as a reaction to wound stimulus. 

 Longitudinal sections of roots of Pastinoca sativa, which were laid hori- 

 zontal in. sand, developed new sprouts on both cut surfaces near the cam- 

 bium. In isolated pieces of bark, sprouts were produced on the inner side 

 and roots on the outer side. The isolated central cylinder formed only 

 roots. 



The experiments with potatoes are very instructive. If any eye at all 

 was left uninjured on some aerial shoot, this developed an aerial tuber. If 



