1912.] 



PUBLIC DOCUMENT — No. 31. 



145 



variations in temperature, and that there wonld also be differ- 

 ences in the flow of sap and the translocation of plastic sub- 

 stances. That this is true is shown bj the fact that trees make 

 more growth on one side than on another, the more or less local- 

 ized photosynthesis causing a greater transmission of plastic 

 substances on that side. 



Some of these experiments were begun in 1907, a part of the 

 observations being made by Mr. IST. F. Monahan, our former 

 assistant, while others were obtained in 1909 and later by Mr. 

 G. H. Chapman. 



These resistances were determined by a Weston Electric Com- 

 pany combination bridge, rheostat and galvanometer, provided 

 with a battery of 6 or 8 large Samson cells. 



Table I. — Showing Daily Records of Electrical Resistance (in Ohms) of 

 Maple {Acer saccharum, Marsh), April 7-26, 1907. Resistances taken 

 on the North, South, East and West Sides of the Tree at Midday. 



[Electrodes 10 feet apart. Mean daily temperatures given in degrees F.| 



April 7, 



Date. 



9, 



10, . 

 11, 

 12, 



13. . 

 14, 



15, . 

 16, 

 17, 



18, . 

 19, 

 20, 

 21, 

 23, 

 24, 

 25, 

 26, 

 Average, 



Tempera- 

 ture. 



East. 



19,000 

 19,500 

 23,000 

 23,000 

 22,000 

 21,000 

 21,500 

 20,000 

 19,100 

 19,500 

 20,500 

 21,500 

 21,000 

 18,000 

 19,500 

 15,000 

 16,000 

 10,900 

 15,700 



19,857 



South. 



18,840 

 19,000 

 23,000 

 23,000 

 21,500 

 21,000 

 21,000 

 19,400 

 18,900 

 19,000 

 20,500 

 23,000 

 20,000 

 18,300 

 19,500 

 14,600 

 17,300 

 17,200 

 15,000 



19,055 



West. 



22,000 

 23,400 

 23,000 

 23,000 

 23,000 

 22,500 

 22,900 

 22,000 

 21,200 

 20,000 

 21,500 

 21,000 

 19,000 

 21,300 

 22,000 

 16,300 

 17,000 

 17,400 

 16,000 



19,310 



North. 



22,000 

 23,000 

 24,000 

 23,500 

 23,500 

 23,000 

 23,000 

 22,000 

 20,800 

 21, .500 

 21,000 

 17,000 

 21,000 

 20,800 

 21,000 

 16,000 

 16,500 

 19,100 

 18,200 



20,890 



