Meyen's Report for 1839 on Physiological Botany. 335 



The delineations which accompany this treatise, are among 

 the most beautiful and correct which have ever been published ; 

 especially those in the 'Annalesdes Sciences Naturelles.' They 

 are not so good in the i Archives du Museum.' 



By new observations I have confirmed the statement, that 

 the bark of trees is not reproduced* ; in a series of cases I had 

 covered barked twigs and young stems with glass tubes which 

 fitted air-tight, and thereby prevented the injurious influence 

 caused by evaporation and the consequent desiccation of the 

 wounded surface. The substance which, under certain circum- 

 stances, is formed on the decorticated wood, and which has 

 been considered as bark, consists simply of a loose parenchy- 

 matous tissue, and is formed out of a gum-like sap exuded from 

 the medullary rays which open upon the decorticated surface. 

 This sap exudes in the form of transparent drops, which, when 

 protected from evaporation, metamorphose themselves into a 

 colourless cellular tissue, which increases more or less accord- 

 ing to the quantity of forming sap exuded by the medullary 

 rays ; sometimes a surface of a square inch or more is co- 

 vered with this bark-like tissue, which proceeds from one 

 point ; and if this formation commences at several neighbour- 

 ing spots at the same time, the masses at length join toge- 

 ther and cover the decorticated wood for a considerable space. 

 This new tissue is, however, not bark, and produces no new 

 wood, and therefore cannot prevent the final death of a tree 

 when it has been barked all round; but in case of partial de- 

 cortication only its rapid production is much to be desired. 



On some specimens I could see that the new layer of wood, 

 with its medullary rays, &c. was formed only on the inner 

 surface of the bark, for the bark which had been separated 

 from the wood before the formation of ligneous matter pro- 

 duced a new ring ; in some places, indeed, a quantity of this 

 bark-like tissue had been deposited between the new-formed 

 ring and the surface of the wood. 



Moreover, I remarked that in eight cases the thick glass 

 tubes which were fastened over the decorticated surfaces were 

 three times broken, and indeed suddenly, and into small 

 pieces, which cannot well be explained by an evolution of va- 

 pour. 



Dr. Becks f has published a treatise f On some Phaenomena 

 in the growth of Dicotyledonous Trees/ in which he explains 

 the formation of those raised signs and figures which one 

 sometimes finds on the stems of trees, when in a former pe- 

 riod they had been imprinted on the wood, as, for instance, in 



* Berichte iiber die Setzung des Vereins zur Beforderung des Garten- 

 baues in dcr Preussischen Staaten, voin 27 October, 1839. 

 t Linnsea, von 1889, 544. 



