210 TRANSPIRATION. 



them together in a dry place, weigh them at intervals daily 

 for several days, and note the loss in weight in each case, 

 due to loss of water by transpiration ; B loses most water, 

 but A loses much more than C (which loses very little). 

 Cut and examine with microscope a vertical section of the 

 peel from B, and note especially the cutinised epidermis. 



(6) That the waxy bloom on many leaves limits the 

 rate of transpiration is easily shown. Take two leaves 

 of Ficus (India Rubber), and to the petiole of each fasten 

 a piece of wire with a loop ; from one leaf (A) wipe oft' 

 the bloom, using a cloth and warm water, and leave B 

 untouched. Weigh the two leaves, hang them up, weigh 

 them two or three times daily, and note that A loses more 

 than B. 



(c) Take two potatoes of equal size. Peel one ( A) so 

 as to remove the corky layer ; weigh the two, place them 

 together in a dry place, weigh daily, and note that A loses 

 much more water than B. Examine thin vertical sections 

 of the peel, and note the cork layer at the surface. 



(d) The slight loss of water from unpeeled Potatoes is 

 chiefly accounted for by the presence of lenticels. Cut 

 two similar short pieces from a twig of Horse Chestnut or 

 other tree showing conspicuous and not too crowded 

 lenticels. With wax seal up in A the lenticels, and in 

 B patches of cork corresponding in size to the lenticels 

 sealed in A. Weigh both pieces, put them in a dry place, 

 and after twenty-four hours note that A has lost less 

 water than B. 



273. Cuticular and Stomatal Transpiration. 



Though various simple experiments show that very little 

 of the water lost by a leaf passes through the cutinised 

 epidermis, especially when the cuticle is impregnated with 

 or covered by waxy substances, it is equally easy to prove 

 that the cuticle is not absolutely impermeable to water. 



(a) Cut off a Begonia or Ficus leaf (or other leaf with 

 a thick cuticle and no stomata on the upper surface), and 

 lay it in a dish together with a glass slide or a watch-glass. 



