Vegetable Physiology for the Year 1836*. 437 



in the bark of the stem, or under the epidermis in the petiole 

 of the leaf, than between the woody cells. If we examine 

 this cellular mass in the stem of Sambucus nigra in diagonal 

 sections, the cellular cavities appear at first sight to be very 

 irregularly distributed in a completely homogeneous glass-like 

 transparent substance ; by a more accurate examination it is 

 however evident that this substance is not totally homogeneous, 

 but that it separates into cellular membranes and into inter- 

 cellular substance. The lines of demarcation are said to be 

 very fine and easily overlooked. 



Our views on this point are very different from those of 

 Mohl. If we take very thin sections, and observe them with 

 a magnifying power of 1000 or 1800, with achromatic glasses, 

 no lines can be perceived distinguishing the exterior surface 

 of the cellular membrane from the intercellular substance; 

 but it can be plainly seen that there takes place a gradual 

 transition from the substance of the membrane of the cell into 

 the so-called intercellular substance. I will also mention an 

 observation which most clearly proves that the intercellular 

 substance of Mohl is no peculiar separately constituted sub- 

 stance, which is as it were diffused between the cells, but that 

 it belongs to the cellular partitions, and is secreted by them 

 when a more close connection of such cells is to take place. 

 If, for instance, we observe in diagonal sections the solid cel- 

 lular layers which clothe the leaf petiole of Beta Cicla (the 

 red variety is best for this purpose), we find that the so-called 

 intercellular substance occurs in great quantities between the 

 cellular layers; we however can distinguish even with weaker 

 magnifying powers that to each one of the surrounding cellular 

 membranes belongs an appropriate portion of that intermediate 

 substance. I could mention several other instances where the 

 case is precisely similar; and consequently his view of the 

 nature of the intercellular substance in vegetables would have 

 to be altered. Mohl also applies his view of the intercellular 

 substance to the epidermis of plants, as he considers the cuticula 

 with its dependents as this substance in which the cells are 

 sunk. 



Subsequently to the appearance of this memoir of Mohl, 

 Valentin * also published a series of observations in which 

 this intercellular substance was demonstrated more or less 

 evidently; and these examples will be multiplied by every ob- 

 server. Valentin concludes from his observations that all in- 

 tercellular substance is found only between ligneous forma- 



* On the Structure of Vegetable Membrane, especially in the secondary 

 ligneous layers ; in his Rcpertorkimfiir Anat. u. Physiol., vol. i. p. 9b*. 

 Berlin, 1836. 



