TRANSPIRATION. 201 



(c) Set a Broad Bean seedling in a bottle, with its root 

 dipping into some red ink. After a time the veins of the 

 leaflets become coloured ; now cut across (1) the portion 

 of the root which was above the ink, (2) the stem, (3) a 

 petiole, and note the red-stained vascular strands. 



(d) To show that the water travels in the xylem vessels, 

 it is necessary to use pigments which will stain the 

 lignified walls, and to examine microscopically thin sections 

 of the stem after it has absorbed the coloured water. The 

 transparent stems of Balsam are perhaps best, but shoots 

 of Sunflower, Broad Bean, etc., will answer. Place the 

 cut shoot in a bottle of water coloured with safranin or 

 eosin, and after an hour (or as soon as the colour has 

 appeared in the transparent stem of Balsam, or in the 

 leaves of other plants) cut thin transverse sections, and 

 note that the xylem of the vascular bundles is stained. 



(e) Set a cut leafy shoot of Lime or other woody plant 

 in water for some time, then transfer it to water coloured 

 with safranin or eosin. After a few hours cut thin 

 sections, atid note that only the vessels and tracheids are 

 stained. 



(/) Repeat the preceding experiment with fairly thick 

 branches of various trees and shrubs, and note that in 

 some cases only the outer part of the wood is stained, the 

 inner portion no longer conducting water. 



N.B. In all experiments with coloured water, in order 

 to ascertain the exact paths of water-conduction, the ex- 

 periment must not be continued too long, otherwise the 

 stain will diffuse into other tissues than those actually 

 concerned in conduction. 



264. The Use of Coloured Solutions, to measure the rate of 

 the transpiration current, is open to objections. It is easy to 

 prove that the pigment is arrested by the walls, while the water 

 passes onwards. Pour some weak watery solution of eosin into a 

 tall jar, and fasten a strip of filter- or blotting-paper to the cork or 

 to a rod placed over the mouth, so that the lower end of the paper 

 just dips into the solution. After a short time note that the paper 

 is wetted above the point reached by the pigment itself. 



