110 ON THE PLANT-CELL. 



towards each other in their direction, in two contiguous cells, 

 manifestly depends upon the association of the cells, since in the 

 Charce, without exception, the current in the one cell corresponds 

 to a current in an opposite direction in the other. 



The fact itself is indubitable, and is readily observed in Chara, and 

 partially also in Vallisneria, &c. : the reason of it is wholly unknown. 

 It shows, however, pretty distinctly, that the necessary conditions of 

 the sap-motion lie altogether or in part external to the cell, and that 

 endosmosis probably has a great share in producing them. We never 

 observe, also, in cells which are in contact with others on all sides, as in 

 Najas and Vallisneria, that the currents cover the whole of the walls, but 

 exist only on two opposite sides, which lie, throughout all the cells, in 

 parallel planes, by which the possibility of the contiguous streams being 

 frequently in opposite directions throughout the plant is explained. The 

 second kind of sap-motion in a network of minute currents is probably 

 connected with a greater degree of independence and disconnection of 

 the individual cells among themselves ; and it is also but very rarely 

 observed in the closed cellular tissue. 



56. The individual cell may, as regards its own vital processes, 

 be already dead, but yet retain its connection with other living 

 cells, and probably also conduce to their vitality, and consequently 

 to that of the whole plant, for some time longer. In this way, 

 probably, the so-called vessels, at the period of the ascent of the 

 sap in spring, are reservoirs for the reception (quite passive) of the 

 superabundant sap, which is not yet fit for assimilation ; but at 

 other times they are receptacles for secreted air: the same with 

 the cells which contain special secretions, &c. 



It is a peculiar condition, and one proceeding only from the high degree 

 of individualisation of the cell, and its association with others into a plant 

 without complete abolition of its own individuality, that it may be so cir- 

 cumstanced as relatively (to itself) to be dead, but, as regards the whole 

 plant, still to be deemed alive. This condition also shows how futile and 

 inapplicable all analogies between animals and plants are, two creations, 

 whose most intimate nature is so entirely different, that almost every 

 comparison proceeding upon the constitution of the elementary organ is 

 a mere delusion of the fancy, without any scientific value. 



II. Peculiarities in the Life of entire Tissues. 



57, It may be stated generally, that the vital processes in 

 each individual cell in the same tissue are identical, or at all events 

 very much alike : thus, similar elements frequently compose the 

 greater mass of the parenchyma ; the alburnum-bundles, the milk- 

 vessels, &c. of a plant, contain the same substances. Important 

 exceptions, however, are also met with ; and we find in the par- 

 enchyma, and in closely contiguous cells of the same form, contents 

 of very different nature ; and in the vascular bundles and elsewhere 



