CH. IV] EOSIN ABSORBED. 95 



(110) Course shown by eosin solution 1 . 



Remove from the potorneter the branch used in ex- 

 periment 109, and place the cut end, for one or two 

 hours, in strong watery solution of eosin, taking off the 

 bark of the part in which the saw-cuts were made, leaving, 

 however, 4 or 5 cm. at the base unpeeled. The course 

 of the fluid as it passes up the stem is now traced by 

 the eosin, the manner in which the colour spreads at the 

 doubly-cut region being of course the chief point to be 

 noticed. The reason for leaving the bark on the terminal 

 4 cm. (which is not an essential precaution) is simply to 

 ensure that any superficial rise of fluid shall take place 

 on the bark instead of on the wood. 



(111) Air-pump. 



Cut a branch of Portugal laurel (Primus lusitanica) 

 of the same size as that used in experiment 109, and select 

 one having a part of about 25 cm. in length bare of side 

 branches; leave it in water for some hours, then cut off 

 the 25 cm. and attach one end of it to a potometer, and 

 the other to a water air-pump. When the air-pump is in 

 action water will be sucked through the branch out of the 

 potometer and readings can be taken with a stop-watch. 

 Adjust the suction of the pump so that the readings of the 

 potometer are roughly the same as those obtained in 

 experiment 109. Now make the two overlapping saw-cuts 

 as explained under experiment 109 and note the result. 

 The point of interest is that here there is no recovery after 

 the depression in rate of absorption, because there is 



1 See the figures iu Strasburger's Leitungsbahnen, p. 601. 



