42 MOTION OF THE JUICES OF THE ANIMAL BODY. 



The most recent experiments on this subject by E. BRUCKE, leave no doubt in 

 regard to the actual state of our knowledge. 



According to DUTROCHET, it is the extremities of the radical fibres, called by DE 

 CANDOLLE, spongioles, which effect the rise of the spring sap; and he believes 

 (L'agent immediat du mouvement vital, Paris,1826,) that the force with which the 

 sap is driven upwards, acts from the root. DUTROCHET cut off a peice of a vine 

 stem, two metres long; and he saw that the sap flowed steadily from the shortened 

 stem in connection with the root. When he had again cut it off close to the ground, 

 he observed the portion in the ground continued to pour forth sap from the whole 

 cut surface. He pursued the experiment, going deeper every time, and he always 

 found that the sap flowed from the part left in the ground, till at last he came to 

 the extreme points of the fibres, in which he then located the origin of the moving 

 force. 



The peculiar activity of the spongioles must, according to DUTROCHET, be 

 ascribed to all the causes, taken together, which determine the phenomena of 

 endosmosis. 



Now that we are better acquainted with the phenomena of what is called endos- 

 mosis, we may oppose to this view some well founded doubts. All observers agree, 

 that the increase in volume of a liquid, separated from another liquid by a porous 

 diaphragm, is determined by a difference in the qualities of the two liquids. If 

 their composition and properties be the same, there is no cause sufficent to produce 

 mixture and change of volume, since in this case, the attraction of both for the 

 diaphragm, and for each other, is perfectly equal. 



In the course of his admirable researches, BRUCKE determined the specific gravity 

 of the spring sap which had flowed from the vine.* He found it, in one plant 

 == 1-0008, and in another,= l-OOO^ 1 ) 



These numbers prove irresistably, that in the specific gravity of the sap of the 

 vine is in no way different from that of ordinary spring water, or of the water 

 which has filtered through garden mould. In most cases, spring water contains 

 even more dissolved matter. 



The spring sap of the vine, which had the sp. g. 1-0008, raised a column of 

 mercury to the height of 174 lines (14-5 inches,) and therefore exerted a pressure 

 equal to that of a column of water 195 inches high. It is quite impossible to 

 account for this pressure by the difference in the amount of dissolved matter in the 

 water absorbed by the roots, and the sap flowing from the cut surface. In the 

 experiment No, IX., of BRUCKE, made with a vine, the sap of which had the sp. g. 

 1-0009 the mercury was raised at 7 A. M., to the height of 209 lines, (nearly 17-5 

 inches. 



No one can doubt that what is called endosmosis has some share in the rise of 

 the sap of the maple and birch trees, which is proportionally rich in sugar, and 

 differs materially in composition from spring water, as well as on the flow or exu- 

 dation of gummy or saccharine juices; but the pressure exerted in these cases, 

 cannot be compared to that exerted by the sap of the vine, where the causes 

 included under the word endosmosis cannot act. 



It is evident, that the cause of the pressure of the spring sap must be transient, 

 called into action by external causes, and limited to a short period.t The experi- 

 ment of DUTROCHET, from which he concludes that the cause of the rise of the sap 

 resides in the extreme points of the roots, may be thus interpreted : " The cause 

 of the efflux and pressure of the sap exists in all parts of the uninjured plant, down 

 to the extreme spongioles of the root." 



The present season does not admit of experiments on this point ; but as spring 

 approaches, it may be proper here to develope more clearly the grounds of the 

 opinion, that the cause of the efflux of the sap of the vine is a transient one. Per- 

 haps some one may thus be induced to decide experimentally all the questions of 

 this remarkable phenomenon. 



( l ) Poggendorf s Annalen der Physik, Ixiii. 177. 



* Observations of BRUCKE on.the specific gravity of the sap of vinos. 



t The cause of the rise of the sap is transient ; and depends on external influences 



