MOVEMENTS OF WATER IN THE PLANT. 



23 



immersed in mercury. (Fig. 19.) The lifting power of transpira- 

 tion can be estimated from the height of the mercury column. 



EXPERIMENT 27. 



ESTIMATION OF THE TRANSPIRATION FROM A SINGLE LEAF. 



Fasten a leaf with around smooth petiole in one end of a U tube 

 by means of a rubber stopper. Previously fill the U tube with 

 water and fit in the other end a long capillary tube bent at right 

 angles. Place the apparatus in such position that the leaf will be 



Fig. 20. 

 b 



Apparatus for estimation of trans- 

 piration. (Mangin.) The water 

 recedes from a toward b. 



held upright, and the long arm of the small tube horizontal (Fig. 

 20). A small amount of transpiration from the leaf will cause the 

 water in the small tube to recede horizontally. The amount and 

 rate of transpiration may be easily computed. 



18. Wilting of Excised Shoots in Water. — Herbaceous 



shoots when cut off and set in water generally wilt quickly, 



but if the shoot is cut under water it remains fresh a much 



longer time. Evidently the cause of the wilting when the 



stems are cut without this precaution is the penetration of the 



shoot by air. Perhaps in rapidly-growing plants escaping slime 



may seal up the ends of the vessels which conduct water. 



EXPERIMENT 28. 



WILTING OF SHOOTS EXCISED IN AND OUT OF WATER. 



Bend a long shoot of a slightly woody plant (Symphytum, Rose- 

 bush, etc.), so that a portion of the stem is under the surface of the 



