212 



LTNK ON CELLULAR TISSUE. 



cells, are often separated from each other, sometimes quite combined, 

 and sometimes partly so. I have found them entirely separated from 

 each other in several parts, especially in fruits j the berries of the 

 Ligustrum, and of the Lantana aculeata, furnish proofs of this. In 

 the midst of the fruit stalks, the receptacles, and some other hollow 

 parts, single cells are often seen. In order to examine the tissue of 

 cells in this respect, it is necessary first to boil the part, because the 

 cells are then easily detached from each other. 



Fig. h 



The oblong cells, taken from the exterior of a French bean, are 

 shown in the figure. I have seen the same thing in the potato, when 

 boiled ; in the roots of parsley, &c. 



We cannot separate the cells in the rind (epidermis) of plants, by 

 this or any other method ; for there they are entirely united. The 

 cells that are found immediately under the rind, are also inseparable. 

 No interval being discoverable between the cells of this kind, it is, 

 therefore a tissue of cells, continued without any interruption. 



In fine, there are cells which are not entirely united. The partitions 

 united with each other in the middle, are separated towards the edge, 

 and leave a little interval, similar to a vein. This structure is gene- 

 rally found in all succulent plants, in the pith, and, in general, in all 

 the fleshy parts. Hedwig was acquainted with these little intervals, 

 and called them vasa revehentia (De Fibrce Animalis et Vegetabilis 

 Ortu, Lips. 1790, p. 23.) M. Sprengel pretends that Hedwig is 

 mistaken, and that he has looked at the lower edge of the partition, by 

 the transparent membranes, beside the upper edge, which causes the 

 appearance of an interval, or vessel. He is right; one may easily be 

 deceived in this ; but on looking obliquely at the tissue of cells, we 



