200 TRANSPIRATION. 



fixed into it, over tumblers half filled 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. 



(d) To demonstrate transpiration from the leaves of a 

 rooted plant, push a leaf of a pot plant into a test-tube, 

 rolling the leaf up if necessary; plug the mouth of the 

 tube with cotton-wool, and note the moisture that con- 

 denses on the inside of the tube. Another plan is to clip 

 or cement a small watch-glass on a large leaf, so as to 

 form a chamber in which moisture may condense. 



263. The Water Channels in Root, Stem, and 

 Leaf. By various simple methods we can demonstrate 

 that the transpiration current passes along the xylem of 

 the vascular bundles. 



(a) G-et leaves with broad thin blades and long stalks, 

 e.g. Lesser Celandine, Tropaeolum, Violet in winter the 

 radical leaves of G-arlic Mustard are useful for transpira- 

 tion experiments, or seedlings can be used. Place them in 

 narrow-necked bottles containing red ink, and note that in 

 a short time the ink runs up in the stalk and colours the 

 veins in the leaf-blade. Good results are obtained by 

 using a shoot with white flowers, the veins in the petals 

 being coloured by the ink ; or by using transparent stems, 

 e.g. Balsam, and noting how the vascular bundles of the 

 stem are stained by the ink. 



(fc) To demonstrate the path of the water in a woody 

 stem, cut two similar leafy twigs, and from a place to- 

 wards the base of each cut a ring of tissue, in one case (A) 

 including only the soft outer tissue as far in as the sticky 

 cambium, but in the other case (J5) including also the 

 outer portion of the wood. In each case cover the injured 

 part with vaseline, and set the two twigs in water ; note 

 that in A the leaves remain fresh, while in B they soon 

 become wilted. Two other twigs similarly treated should 

 be set in red ink ; after some time see whether the ink has 

 reached the leaves. 



