211 



It is shown that the water in the vascular bundles in the stems 

 of tall trees, when not subjected to pressure upwards from below, 

 must be in a state of tension. "Therefore when root pressure is 

 not acting and when the leaves of trees are transpiring, the 

 cohesion of their sap explains fully the transmission of the tension 

 downwards, and consequently explains the rise of the sap." 

 For example, in a tree loo meters high there results a tension of 

 20 atmospheres, but the cohesion of sap has been experimentally 

 shown to be at least 200 atmospheres; therefore it "is in no way 

 taxed by this tension." 



The author finally points out that, in such tall trees, the 

 osmotic pressure, necessary to keep the cells in the mesophyll 

 turgid, must equal in magnitude the tensions necessary to raise 

 the sap; and that "the stored energy set free by respiration in 

 leaves is quite sufhcient to do the work of secretion against the 

 resistance of the transpiration stream; while, when the vapor 

 pressure of water in the surrounding space is low, and when 

 evaporation is doing the work of raising the sap, the expenditure 

 of energy in this process will reduce the quantity of water evap- 

 orated only by an imperceptible amount." 



C. Stuart Gager. 



NEWS ITEMS 



Ernst Ule died on July 15 in Berlin-Lichterf elder after a short 

 illness at the age of 61 years. He was known chiefly for his 

 exploration of the Brazilian flora. 



Professor T. D. A. Cockerell is anxious to get living material 

 of Helianthus , from eastern and southern United States. Those 

 who could collect such material will confer a favor by writing to 

 Professor Cockerell at Boulder, Colorado. 



Dr. H. S. Jackson, professor of botany and plant pathology at 

 the Oregon Agricultural College, has accepted the position of 

 chief in botany at Purdue University Experiment Station, 

 beginning Sept. i, 1915. He will be succeeded by H. P. Barss, 

 formerly associate professor of botany and plant pathology at 

 the Oregon Agricultural College and Experiment Station, 



