798 



all tissue down to the cambium, have been the subject of observation for 

 more than lOO years. 



Thus Treviranus^ quotes that L. Firsch found some apple and pear 

 trees on an estate in the Province of Brandenburg, from which all the bark 

 had been removed from the points of insertion of the lowest branches down 

 to the roots, completely around the trunk, so that the white wood could be 

 seen everywhere. The trees were covered again with new bark. Frisch 

 assures us that this experiment will always succeed if made at the time of 

 the solstice and if the exposed outer surface, over which the sap is spread 

 uniformly with a feather, is protected by linen or split cane against the sun 

 and wind*. 



The celebrated experimenter, DuhameP, removed a ring of bark from 

 several young trees, elms, plums, etc., 7 to 10 cm. wide down to the wood, at 

 the time when the sap was flowing and surrounded the wounds with glass 

 cylinders, which were closed at the top and bottom against the uninjured 

 part of the trunk with cement and tissue. He found delicate, jelly-like 

 warts forming on the exposed wood surface, and pushing out between the 

 wood fibres of the sap wood (des mamelons gelatineux qui sortaient d'entre 

 les fibres longitudinales de I'aubier). These little warts, which push out 

 under very tender, probably left over, phloem lamellae, were at first white, 

 and half translucent, later gray, and after 10 days (on April i8th) green. 

 These new structures, broadened in the course of the summer and finally 

 uniting, produced a rough bark beneath which delicate wood lamellae were 

 recognizable. "Ainsi il est bien prouve que le bois pent produire de I'ccorce 

 et que cette ecorce est des lors en etat de produire feuillets ligneux ..." 



Knight made similar experiments and obtained similar results. He 

 found once'' on Ulmus montana, a regeneration of the bark when the wound 

 had not been covered. The tree grew in a shady place. Knight found in 

 old topped oaks, with an incompletely formed new bark growth, that the 

 jelly-like w^arts had pushed out from the parenchymatous cell tissue and "in 

 many cases new bark was formed in small and isolated portions only on the 

 upper surface." 



Meyen* cjuotes W^erneck's observations, according to which the regen- 

 eration of the bark will take place only if the barking happens about the 

 25th of June, when the trunks are still young and the wounded place is 

 "very carefully protected against drying by a hollow and closely adjusted 

 bandage." 



We find Meyen's own theory-'' in the description of his experiments 

 given in his Phytopathology. On April 30th, 1839, in warm sunshine he 



1 Treviraniis, Physiolog-ie der Gewachse, Vol. TI, 1S3S, p. 222. 



2 Duhamel, Physique des arbres 1758, Vol. IT, p. 42. Vol. VII, p. 63, and loc. cit., 

 p. 44. Vol. VIII, p. 66, 67. 



3 Treviranus, loc. cit, p. 223 (Beytr. 223). 



4 Meyen, Neues System d. Pflanzenpliys. 1837, p. 394. 



5 Meyen, Pflanzenpatliologie, published by Nees. v. Esenbeck. Berlin 1841, p. 14. 



Miscell. Berolin. Contin, II (1727), 26. 



