BRIGGS: THE LIVING PLANT AS A PHYSICAL SYSTEM 107 



would be proportional to rfia?. According to Brown and Es- 

 combe the diffusion would be proportional to n\/a. While it is 

 evident that in this comparison we are not fulfilling one impor- 

 tant condition imposed by Brown and Escombe, namely, that 

 the pores shall be sufficiently far apart to avoid interference in 

 the diffusion stream lines, the two conclusions are at such great 

 variance as to invite a further examination of the diameter law. 



The ascent of sap. We have to consider finally the means by 

 which the water is lifted to the tops of the highest trees, amount- 

 ing in the case of the Sequoia to a distance of 300 feet above the 

 ground. 



Strasburger, 9 by poisoning the cells of various plants, has 

 shown that the living elements of the wood play no essential 

 part in the elevation of the water. An oak nearly 22 meters 

 high cut off obliquely at its base and set in a picric acid solu- 

 tion was found to take up the poisonous solution readily. After 

 the acid had reached a height of 15 meters and the topmost 

 leaves had changed markedly in appearance, fuchsin was added 

 to the picric acid solution. At the end of nine days the highest 

 branches were found to be impregnated with picric acid, which 

 had been drawn up to a height of nearly 22 meters. Fuchsin 

 also was found in these branches, although preceded by the pic- 

 ric acid by three days. This experiment, then, demonstrated 

 that water solutions can rise in trees without the assistance of 

 living cells to heights far above those that can be accounted for 

 by atmospheric pressure. Strasburger also found that stems of 

 plants killed by subjecting them to a temperature of 90°C. 

 were still capable of raising water to a height of 10.5 meters. 

 We may, therefore, conclude that vital processes are not essen- 

 tial to the ascent of sap. 



Of the numerous theories which have been advanced in ex- 

 planation of this phenomenon, that of Dixon and Joly 10 alone 

 appears to be physically sound. According to these authors, 

 sap rises through the trunk of the tree as the result of evapora- 



9 Strasburger, E. Ueber das Saftsteigen. Histol. Beitr., 5: 10. 1893. 

 10 Dixon, H. H., and Joly, J. On the ascent of sap. Phil. Trans., 186b: 563- 

 576. 1895. 



