<;i 



sure which corresponds to tlic rate of flow in tapped trees. By 

 employing self-recording gages and thermometers complete 

 seasonal records have been obtained which reveal a striking 

 parallelism in the fluctuations of pressure and of temperature. 

 This has led some to explain the phenomenon of sap pressure 

 and flow as due simply to the expansion with rise of temjierature 

 of the gas imprisoned within the woody tissues ; but the fluctu- 

 ations observed in pressure and suction are far greater and more 

 sudden than this physical explanation can account for. Thus 

 variations are frequent in these gage records of ten or fifteen 

 pounds pressure with a change of but a few degrees in tempera- 

 ture. Extreme fluctuations are recorded of nearly thirty pounds 

 to the square inch, within twenty-four hours, viz., from 5 pounds 

 suction to 22 pounds pressure. A rise of over twenty pounds 

 in pressure was observed with a rise in air temperature of only 

 two degrees, which would mean even less increase in tree tem- 

 perature. The conclusion is that sap-flow in the sugar maple is 

 a true bleeding phenomenon, attributable to the vital acti\'ities of 

 living cells. The pressure shown by the gage is simply a partial 

 expression of the energy of the countless living, working proto- 

 plasts of the maple stem. 



There is little evidence of "root-pressure" ; in fact on good 

 " sap days" the flow into the tap hole comes chiefly from above 

 downwards. We must regard the stem tissues as chiefly active, 

 the cells in the vicinity of the tap hole operating alternately as 

 suction and force pumps, so to speak, sucking the sap from root 

 and remoter stem tissues and forcing it out through the tap hole. 



It is not difficult to conceive how a rise of temperature past a 

 critical point for their vital activities should arouse or stimulate 

 the bleeding activities of the cells and how a fall below this point 

 should check them. The suction thereupon developed would 

 seem to be due to osmotic reabsorption of the exuded sap by the 

 same cells. L. R. Jones. 



PROCEEDINGS OF THE CLUB 

 Wednesday, February 24, 1904 



This meeting was held at the New York Botanical Garden ; 

 Professor Underwood in the chair ; sixteen persons present. 



