MOTION OF THE SAP THBOUGH PLANTS. 523 



the latter is naturally and by degrees clothed with apricot- wood*; for out of 

 the same soil an apricot-tree would merely take up the same crude sap as 

 the plum-tree ; but afterwards, in proportion as the leaves and branches 

 of the plum-tree, or of the apricot, evaporate, assimilate, &c., plum or 

 apricot-wood will remain. For these facts there is less apparent need of 

 the fabulous bark-sap than in the former case. It is, indeed, unnecessary 

 to treat of the various speculations, and on the especial motions of the 

 bark -sap, or the causes of its motion, &c. A close microscopic investi- 

 gation entirely suffices to show that in the parenchyma of the bark there 

 does not exist any general matter capable of organisation, and that in the 

 liber-cells, air, solid resinous matters, or milk-sap, are principally present. 

 Nor is it worth the trouble to investigate the copious statements concerning 

 the movements of the bark-sap, from the outer to the inner parts of the 

 trunk through the medullary rays ; nor to discuss, what is evidently so 

 imaginary, that no one has experimented thereon or can do so. It is very 

 evident, however, that the cells of the medullary rays generally have 

 contents differing from those of the parenchyma of the bark, also from 

 those of the liber. 



I have already spoken of the meaning of the word "gland " with regard 

 to plants. Here we touch on a subject connected with it, namely, the 

 segregation of certain substances in an intercellular sap-passage, which in 

 two ways require further explanation : 1. By what means so large a 

 quantity of cells are destined to form gum, jelly, or oil, and to deposit them 

 in their different canals ; 2. The process of the secretion itself. It is a 

 fact, that in this case the single cells have the same relations as though 

 the walls of the intercellular spaces formed the outer surface of the plant ; 

 but the difficult point is the apparent impossibility of evaporation from 

 sap-passages surrounded by water. 



The complicated relations of the milk-sap to the neighbouring cells, 

 from which it yet must be secreted, is still more doubtful to us, since we 

 do not yet know the cause of the secretion, the manner of its origin, nor 

 its relations to other cells, &c. ( 319.) 



I have now to speak of resorption. The fact is well known to every 

 attentive observer, nothing needs to be added on this subject. Of the 

 cause of the taking up of the fluid, especially in the spiral vessels, we are 

 entirely ignorant. I have often used the word resorption when speaking 

 of this circumstance. Link ridicules this, because there are no resorbing 

 vessels in the plant, and thinks that I intended by this a fluidifying or 

 organic melting (Wiegrnann's Archiv, vol. ii. 1841.) ; this objection 

 brings strongly to one's mind the obscure physiological notions of the last 

 century. Coagulated blood, plastic exudations, cells, and masses of 

 cellular tissue, must, through chemical processes, have first become fluid 

 before they could be absorbed. In this process the absorbents (lymph- 

 vessels) in animal bodies take no part, neither is the idea of resorption 

 connected with them. It consists in a removal of the fluid from the place 

 where it is deposited, and an absorption into the general mass of sap. 

 Absorption cannot take place in invertebrate animals through the 

 absorbing vessels, because they do not exist. It goes on even in verte- 

 brate animals, as in the serous cavities, but not by means of the lymphatic 



of the lower end is made to absorb, sufficient proof is afforded that no descending bark- 

 sap exists. These facts are frequently used to support the theory, that the existence of 

 a downward movement of the bark-sap., neither the movement nor the sap being demon- 

 strable, is not dependant on gravity, but on a living vital power. 

 * Although universally thus stated, it is not the fact ( 204.). 



