30 HOFFMANN ON THE CIRCULATION 



9 inches in diameter and bled only three days. Neither does 

 the height of the orifice above the soil explain the phaenomenon, 

 for the period of bleeding differed much at equal heights, as 

 No. 8 and No. 4 show. Just as little influence is exerted by the 

 aspect of exposure. 



On the other hand, the higher or lower position of the trees 

 appeared to have an essential influence hydrostatically, They 

 all stood on the southern slope of a hill 30 feet high, in the 

 Botanic Garden at Giessen, in the following order, from above 

 downwards : — 



«, No. 8, which bled 3 days. 



b, — 2, 5 . . 



5+3 days. 



c. 



6, 



d, - 3, 



— 7, 



e, — 4, 



4 

 2 



7 



10 



No. 4 stood 5 feet above the bottom of the hill, and was 

 35 feet high ; the rest were only about 27 feet, in spite of their 

 unequal diameter. This difference of height also appeared to 

 have some influence. 



The epochs of tapping the different trunks were not far enough 

 apart for me to ascribe any considerable importance to that point. 



9. A trunk of Acer campestre, \\ foot in diameter (at the 

 bottom), was tapped at equal depths of 1 inch, in two places, at 

 3 o'clock on the 5th of March, and the exuding fluid all collected 

 (as in all cases, with care that no rain-water should penetrate) : — 



A, orifice 1 foot from the ground, south side. 



B, the same, north side. 



By about 5 o'clock A had delivered l|^ths of a cubic inch, B 

 also IJ^ths. 



From that time till 8 a.m. on the 6th of March not a drop 

 flowed out. About 2 o'clock there were 13fths cubic inches in 

 A, and 19J cubic inches in B. At 5^ 30^ there was i a cubic 

 inch from each. On the 7th at 8 o'clock there was no fluid. 

 At 2 o'clock there was ^th of a cubic inch at A, ^ a cubic inch at B. 

 At 4 o'clock no more had flowed out ; neither was there any at 

 2 o'clock on the 8th. From the little that the short duration of 

 the bleeding allowed to be observed here, the north side would 



