32 HOFFMANN ON THE CIRCULATION 



March 10. 7 o'clock, at A, 3 cub. in. ; at B, 1 cub. in. 



- .. H ... 



.. 5 



11. 7 



..2 



- .5* 



12. 7 



..2 



..5 



13. 7i 



. . 2 



. . 5* .... 4^ a few drops. 



14. 7i .... 13| ditto. 



..2 .... 23 . . 2| cub. in. 



. . 5 .... 1 none. 



15. 7% ... none none. 



..11 .... 5 i cub. in. 



From this it follows that the efflux, or fulness of sap, is greater 

 in the lower part of the stem than further upwards. This 

 phenomenon is not hydrostatical (as a barrel emits a more pow- 

 erful stream from a hole nearer the bottom, than from one at the 

 top, on account of the higher pressure of water), but depends 

 on the force of the water making its way upwards, as is seen by 

 a comparison with Experiment No. 1. It is also again seen 

 what an obstacle the nightly cold is. Lastly, a comparison of 

 the temperatures of the air in the sun, which I observed, shows 

 how much the ascent of the sap is favoured by the heat of the 

 air. 



From the following table, especially from the two last columns, 

 it is seen that on the whole the outflow runs parallel with the 

 temperature. The 10th of March alone forms an exception, evi- 

 dently on account of the unusually favourable weather on the 

 9th, the after-influence of which is seen here. 



