116 WATER- ABSORPTION AND TRANSPIRATION. 



the same in all three bottles at first ; after some hours' exposure to 

 light compare the amounts of water left in the bottles. Which loses 

 most water, and which least? 



* (b) Fix a long-stalked leaf (or the upper part of a Broad Bean or 

 shoot, e.g. Dead Nettle) in a card, passing the leaf-stalk (or the stem) 

 through a hole in the middle of the card and scaling it up with putty or 

 plasticine. Place several cards, each with a leaf or shoot fixed into it, 

 over tumblers nearly tilled with water, and over each of these tumblers 

 invert a dry empty tumbler, resting on the card. Notice the drops 

 of water formed on the inside of each empty tumbler, by condensation 

 of the water- vapour given off by the leaves. Ascertain whether any 

 water- vapour is given off when (1) the upper surface, (2) the lower sur- 

 face, of the leaf is smeared with vaseline to block the stomata. 



* (c) Get any leaves with broad, thin blades and fairly long stalks 

 e.g. Lesser Celandine, Garden Geranium. 1 Place them in bottles of 

 red ink, with the cut lower end of the stalk dipping into the ink, and 

 note the coloration of the veins. Cut a Grass shoot above the creeping 

 stem, and try the same experiment, noticing the parallel arrangement 

 of the veins, as indicated by the red lines which appear in the leaves in 

 a day or two ; a Maize or Wheat seedling may be used. 



(d) The sucking force exerted by the leaves can be demonstrated by 

 attaching a leafy branch, cut under water, to a tube filled with water 

 and dipping into a coloured solution. It will be found that the latter 

 ascends the tube even when the latter is many feet in length. 



Get a branch of Willow in which the young leaves have become fully 

 expanded, and attach it by means of a piece of stout indiarubber 

 tubing to a glass tube about 9 ins. long, with the end farthest from 

 the branch bent at right angles for about 2 ins. Arrange the branch 

 vertically, the longer limb of the glass tube horizontally, and the short 

 terminal part dipping into water tinged with red ink. It is best to cut 

 the branch and attach the tubing under water in a large basin, so as to 

 prevent the entrance into the stem of air-bubbles, which would diminish 

 the flow of water. Lift the glass tube out of the water when the 

 branch is fixed up, and notice that the coloured water soon begins to 

 travel along the horizontal tube. This apparatus may be used to 

 roughly measure the rate of the transpiration current. 



(1) Ascertain whether the flow is different on bright and on dull 

 days, and (2) whether it is influenced by opening door and window so 

 as to cause a draught. What is the e fleet of smearing the surfaces of 

 the leaves with vaseline? On different branches smear (1) the upper 

 surfaces, (2) the lower surfaces, (3) both surfaces, of the leaves, and 

 note the rate of the transpiration current in each case. 

 * (e) A useful piece of apparatus for observations on transpiration is 

 the potometer. The essential part of the apparatus is the potometer- 

 tube (Fig. 42 A), a straight tube (a) about half an inch in diameter with 



1 In winter the long-stalked heart-shaped leaves of Garlic Mustard 

 are very useful for experiments on transpiration. In spring use leaves 

 of Lesser Celandine or Violet. 



