834 



SCIENCE. 



[N. S. Vol. XVI. No. 412. 



The sap rose steadily, and when the tube 

 added was filled, another was attached in the 

 same way, until the upper tube reached the 

 ceiling of the room. In making attachments 

 a break occurred at the first joint above the 

 stem, resulting in a loss of sap down to that 

 point. The break was repaired and the ex- 

 periment continued. Another accident hap- 

 pened at the same joint when the sap was 

 over six feet high, resulting in a further 

 and more considerable loss of sap. On 

 August 14 the sap stood nine feet ten 

 inches high in the tube. The total amount 

 of sap that passed through the plant into 

 the tube was 165 c.c, taking into consid- 

 eration the loss by accident, and estimating 

 the whole tube as of uniform bore, making 

 no allowance for the greater volume where 

 the sap was in contact with the rubber 

 tube. The flower-pot stood in a plate in which 

 a little water was poured every other day. The 

 soil in the pot was watered from time to time, 

 so as to keep it moist, and in a condition 

 under which the plant would most lilcely 

 thrive best. It will be noticed that the plant 

 was under these abnormal conditions thirty 

 days, and that, so far as could be learned from 

 the appearance on August 14, and from the 

 fact that the sap in the tube kept rising, the 

 plant seemed to be alive. The force that 

 caused the ascent of sap in the tube, and that 

 which kept the column at the height men- 

 tioned, is certainly due to some property of 

 the living Begonia. A plant under similar 

 conditions, but first killed by heating, will 

 produce no ascent of liquid, and since it can 

 not be produced by soil and the tubing, we 

 must look for the causes in the living plant. 

 This ascent is probably due to what we call 

 'root-pressure,' and, as root-pressure is ac- 

 counted for by an osmotic pressure resulting 

 from the sap in the cells of the roots and 

 root hairs, the conclusion is that the sap in 

 the tube was forced nine feet ten inches high 

 and kept there by an osmotic pressure of the 

 cell sap. But it can scarcely be wholly due 

 to osmotic pressure, because the sap in the 

 glass tube proved to be a solution too dilute, 

 and this in the tube must be more concen- 

 trated osmotically than that in the roots, in 



order that sap may be transferred from cell 

 up through the plant. When we say too 

 dilute we are estimating concentration and 

 pressure from van't Hofi's law relating to 

 substances in solution. 



This ascent of sap in the Begonia — a plant 

 about fourteen inches high — is an illustration, 

 to some extent, of the tension to which the 

 cells of plants are subjected in the normal 

 condition of life. If there be a pressure in 

 the plant equal to a colmnn of water nine 

 and three fourths feet high, and the plant 

 be only fourteen inches high, the cell tension 

 in the top leaves would be a pressure of eight 

 feet at least. 



Reasoning from this condition of affairs 

 in this plant, it may be that — if the turgor 

 in the leaves of tall trees is as great as that 

 in the Begonia — the forces have to be suffi- 

 cient to sustain a column of water eight feet 

 higher than the top leaves of the plant. 

 Moreover, in view of experiments of Morse 

 and Frazer,* plant sap may exert an osmotic 

 pressure far in excess of that which it would 

 have, according to van't Hoff's law : ' The 

 osmotic pressure of a siigar solution has the 

 same value as the pressure tha^t the sugar 

 would exercise if it were contained as a gas 

 in the same volume as is occupied by the 

 solution.' Morse and Frazer have shovm that 

 a normal solution of cane sugar exerts a pres- 

 sure of 31.5 atmospheres at least. They esti- 

 mate that the pressure could not be less than 

 33 atmospheres, their cell having been shat- 

 tered at a pressure of 31.5. 



Now, according to van't Hoff's law, a nor- 

 mal solution of cane sugar should exert a 

 pressure of not more than 23 atmospheres, 

 unless sugar dissociates; but, -as far as is 

 knovsTi, sugar does not dissociate in aqueous 

 solutions. The results of Morse and Frazer 

 present to the botanist some very striking 

 suggestions, and it may throw some light 

 upon the ascent of the Begonia sap in the 

 glass tube in our experiment. 



That there is some force beyond that indi- 

 cated in van't Hoff's law seems evident, from 

 Morse and Frazer's experiment. Osmotic 

 pressure, according to this law, does not ac- 



*Am. Chem. Jour.,-2S: 1. July, 1902. 



