799 



removed the bark from the little trunks and larger branches of the hazlenut, 

 the snowball, Syringa and willow and, like Duhamel, enclosed the barked 

 places with cemented glass tubes, which in addition were wrapped with 

 paper, although he made the experiments in thickly shaded places. Jelly- 

 like drops were "sweated out" here also, "which always occurred on the 

 places where the medullary rays appeared on the upper surface of the 

 wood." 



Microscopic investigation of this "sweating" showed the warts to be 

 composed of tender cell tissue, "which enlarged constantly because of the 

 gum in the sap, exuded by the medullary ray cells." 



The greenish color, which these new structures assume, arises from the 

 chlorophyll grains. In the course of the experimental year these structures 

 reached a thickness of ii mm. but shrivelled greatly when dried. 



Meyen cannot ascribe the significance of bark to these new structures, 

 which are also produced naturally in shady places^. For "no separation into 

 different layers, of which the normal bark of the same tree is composed, can 

 be seen and moreover there is no trace of sieve tubes in it, which are, of 

 course, very important ..." 



This physiologist, very distinguished in his time, who according to the 

 Mirbelian theory considered the cambium to be a structureless sap, which 

 brought forth such cell structures as those from which it had appeared, has 

 indeed the merit of having made use of the microscope to investigate the 

 new structures which appeared with the healing of bark wounds. He was 

 not fortunate enough, however, to observe the production of wood among 

 these new structures and to prove the analogy between these forms and 

 normal bark. 



Probably the moist air and heavy shading from his cylinder were to 

 blame, since as we shall see these factors influence considerably the charac- 

 ter of the new structure. 



Dalbret^ experimented earlier than Meyen, for on the 21st of June he 

 barked an ash and a walnut, enclosed the barked places in a cylinder and 

 obtained the same results as Duhamel. 



Th. Hartig^ in the spring of 1852 at the time the new annual rings had 

 begun to develop removed the bark from 30 to 40 somewhat older oaks for 

 6 to 8 meters above the ground and in August found the majority of the 

 mutilated trees bore as dense foliage as the adjacent ones from which the 

 bark had not been removed. On 5 or 6 young trunks a scabby eruption, 

 pressed out from the medullary rays of the wood, had formed "curiously" 

 only on the sunny side. Anatomical investigations showed that the erup- 

 tion, quite independent of the phloem and cambium, had come from the 

 wood alone and was a product of the medullary rays. 



1 Pflanzenphysiologie, Vol. 1, p. 390. 



- Journal de la societe d'agronomie pratique 1830; quoted by Trecul in 

 "Accroissement des vegetaux dicotyledones ligneux." Annales des sciences natur. 

 Ill, Serie, Vol. XIX, Paris 1853. 



3 Th. Hartig. Vollst. Naturgesch. d. forstl. Kulturpfl. Deutschlands. Berlin 1852. 

 Explanation of the figures (plate 70, Pigs. 1-3). 



