24 HOFFMANN ON THE CIRCULATION 



only gave a reaction, which was moreover very weak ; the trans- 

 verse section displayed a few light blue bleared spots in the 

 wood ; the liber and bark were unaffected. Longitudinal sections, 

 on the contrary, displayed at particular spots, very sparingly, 

 sharply denned blue points or even streaks (some of them in 

 the direction of the medullary rays) ; microscopic examination 

 showed that the few places in which some of the absorbed sap 

 still remained, were tracheae (spiroids) and the neighbouring 

 prosenchyma of the wood. In the middle fragment, 10 feet 

 above the ground, the cross section gave the same result as 

 before; longitudinal sections led to none. 



5. On a young sycamore, with a trunk 4^ inches in diameter, 

 a branch A, arising 7 feet above the ground on the north side, was 

 bent down to a certain degree and fixed in this position, the 

 outer part cut off, and the point of the portion remaining attached 

 to the stem, dipped 4 inches deep into a cylindrical glass full of 

 solution of the ferrocyanide. A hole B was bored, 1 inch deep, 

 1 foot above the ground on the south side of the trunk. This 

 was done on the 2nd of March. On the 3rd the branch A 

 had absorbed all the fluid, as far as it dipped in it ; the glass 

 attached under B was filled with watery fluid, which did not 

 react with salt of iron. On the 5th the glass at A was refilled. 

 On the 4th the vessel at B was only half-filled; on the 5th 

 again quite filled ; rain which fell on the 4th seemed to have 

 increased the flow of the sap. By the 7th (warmer weather 

 than the 6th) the glass A had been again emptied, and was filled 

 anew. On the 9th again empty, but up to this day, when the 

 efflux at B ceased, no ferrocyanide could ever be detected in 

 the fluid poured out. On this day therefore a new hole C was 

 bored at the same height as B, on the north side of the trunk, 

 corresponding to the absorbing branch A ; and in spite of B 

 having stopped, fluid was poured out freely at C, which on the 

 10th reacted deep blue with the iron salt; the glass A was 

 emptied down to a quarter of its contents (it held altogether 

 about 1 cubic inch). On the llth the freshly effused fluid ex- 

 hibited a very strong reaction. 



The here evidently strong suction of a cut branch, or of a cut 

 root, as in Experiment 1, thus both in the ascending and de- 

 scending directions) results from the pressure of the atmosphere. 



