MKM..IK XXVI.] CAPILLARY ATTRACTION, ETC. 



distribute them, mechanical motion has to take place. 

 This, in the more highly organized plants, goes under 

 the designation of the flow of the sap. 



The flow of the sap in plants and the circulation of 

 the blood in animals are probably due to the same 

 physical cause. And bringing into view the experi- 

 ments already related respecting capillary attraction, I 

 considered, in the work above referred to, the conditions 

 necessary for producing a continual flow, such as evap- 

 oration, decomposition, solution, developing the general 

 law of those movements, and illustrating the great force 

 with which they are accomplished. I showed that these 

 motions depend on this physical principle : " That if two 

 liquids communicate with one another in a capillary 

 tube, or in a porous or parenchymatous structure, and 

 have for that tube or structure different chemical affin- 

 ities, movement will ensue; that liquid which has the 

 most energetic affinity will move with the greatest veloc- 

 ity, and may even diive the other liquid entirely before 

 it ;" and that this is due to common capillary attraction, 

 which, in its turn, is due to electric excitement. 



Applying this principle to the case of plants, the 

 liquid of which the ascending sap is constituted is de- 

 lived from the ground by the action of the spongioles, 

 and consists of water holding in solution the different 

 saline bodies necessary to the plant, along with carbonic 

 acid, etc. This passes upwards by the woody fibre and 

 ducts of the alburnum, making its way to the leaf, on 

 the upper surface of which, in common cases, a change in 

 its chemical constitution occurs through the influence of 

 the sunlight. It obtains a quantity of carbon. This 

 elaborated sap, or latex, now returns to the bark, and 

 descends through its cellular tissue and intercellular 



O 



spaces, finding its way by the route of the medullary 

 rays to all parts of the plant. During its descent the 



