54 Prof. Meyen's Report of the Progress of 



give to the stem an irregular rugged surface. The sub- 

 stance thus originated is the cork, which, as is well known, is 

 applied to such various uses. We can perceive in every cork 

 that its increase took place in layers; and that at the limits of 

 the two layers the cells become rather smaller, and with thicker 

 membranes, from which circumstance these spots appear 

 darker, just as the external ends of the annual rings of the 

 Conifera;, We may always perceive that the annual rings in 

 the wood of trees also exhibit very various and thick layers, 

 that they are often irregularly deposited in thick masses. 

 In cork this is by far more the case. In the cork-oak the 

 bark falls off' every eight or nine years, and is taken off" some 

 years sooner for useful purposes. De CandoUe is of opinion 

 that it is the cellular envelope which is here developed. 



With this development of the cork substance in consequence 

 of age, the development of the third and fourth layer goes on 

 at an equal rate ; the cellular envelope however increases but 

 in a small degree, and without the formation of new layers, 

 while the groups of colourless cells, which often contain cry- 

 stals, increase more and more in circumference. The inner 

 layer develops new fascicles of liber, and the cells situated 

 between the fibres are like those of the cellular envelope, in 

 which, as Duhamel had previously stated, they are immedi- 

 ately continued. 



Dutrochet* has published some observations on the forma- 

 tion of the cork substance ; he especially directs attention to 

 the fact that the increase of this mass takes place towards the 

 interior, as in the corneous tissue of animals. Dutrochet also 

 finds it very necessary to determine closely the external enve- 

 lope of the bark, and in this he follows the statements of 

 Brongniart, since he divides the epidermis into the cuticula 

 and the cellular membrane. I stated my own opinion on this 

 subject in a recent memoir in the second part of this ArcJiiv, 



The development of the cork substance in Acer campestre 

 is quite similar : here it arrives at perfection even in the first 

 year, immediately after which the epidermis splits at various 

 points. In this case then the development of the cork proceeds 

 very rapidly, but it also ceases sooner than in the cork-oak, 

 and in later years the two other layers of the bark are then 

 developed in such a manner that there gradually re-originates 

 a certain symmetry between the individual layers. 



In other cases, as for instance in Banksia serrata, we also 

 find four cortical layers ; but here it is especially the cellular en- 

 velope that enlarges, while the cork substance and the fibrous 



* Formation du Lxkge.—UIrutitut, No. 192. 



