[ r,3 ] 



XV. A Report of the Progress of Vegetable Physiology 

 during the Year 1836. -Sy J. Me yen, Professor of Botany 

 in the University of Berlin,* 



[Continued from p. 537.] 

 On the Structure and Growth of the more perfect Plants, 



IVTOHLf has published a very interesting work on the struc- 

 ^^ ture and development of the bark in the stems of dico- 

 tyledons, in which this subject has been treated comparatively 

 in various plants. The experiments of Mohl are as follows : 

 In the bark of a young branch of the cork-oak (Qiiercus Suber) 

 four distinct layers are to be distinguished. The exterior layer 

 is the epidermis ; it consists, as in other cases, of a simple layer 

 of flat thick-sided cells, and is dotted with star-like hairs. 

 (De Candolle, it is true, observes that the epidermis of trees 

 is never covered with hairs.) The second layer lies close un- 

 der the epidermis, and consists of 3 — 5 strata of thinner-sided 

 cells, void of colour and of granules, which are for the most 

 part deposited horizontally, and are also like the cells of the 

 epidermis, rather compressed (i, e. towards the surface of 

 of the stem). The third layer is a cellular envelope, which 

 appears as a green parenchymatous layer of cells. In this 

 layer of green cells appear single, colourless, rather larger cells, 

 which contain small granules also void of colour ; a circum- 

 stance which is also to be found in many other plants. The 

 inner or fourth layer is the liber or fibrous layer, which how- 

 ever is only recognised as a distinct layer in branches of some 

 years* growth. In branches from two to three years old of 

 this plant we find the above-mentioned layers of the bark 

 scarcely changed : the epidermis and the second layer are un- 

 changed ; the parenchyma, on the other hand, of the cellular 

 envelope is enlarged ; the cells have become thicker, and we 

 find dots on the partitions. First, in the third and fifth year, 

 the epidermis, which can no longer follow the expansion of 

 the bark, and in general of the mass of the young branch, ac- 

 quires small cracks, and now a great change takes place in 

 the layer of cork situated under it. This layer, which at first 

 was so small, enlarges on the inner side by depositions of new 

 layers. The new layers consist, like the old ones, of thin- 

 sided colourless cells, but He with their longer diameter of their 

 length in the direction of the bark. With this continual in- 

 crease in size of the interior layers, the exterior ones split, and 



* From Wiegmann's Archiv fur Naturgeschkhte, 1837, Part 3. Trans- 

 lated by Mr. Wm. Francis. 



t Observations on the development of cork, and of the bark on the rind 

 of arborescent dicotyledons. — Tubingen, 1836. 



