200 



TRANSPIRATION 



Ex. 116. — (a) Dip the petiole of a leaf of elder in a weak solution of eosin 

 or red ink and place the whole in a bright situation. After an hour hold the 

 leaf up to the light and examine with the naked eye or a pocket lens ; the 

 solution is absorbed and travels along the vascular bundles which will be 

 seen to be coloured red. 



Cut thin slices of the petiole and observe with a lens that the solution has 

 not diffused much into the tissues round the vascular bundles. 



{6) Repeat the experiment with other leaves and herbaceous leafy stems. 

 [c] Dip the peduncles of snowdrops, pansies, crocuses, narcissi and other 



flowers in the solution and note that 

 the thin vascular bundles in the petals 

 become stained red. 



Ex. 117. — Remove a ring of bark, 

 i an inch wide, from the branch of a 

 tree in summer and note that the leaves 

 above the cut do not wither. 



Ex. 118. — To show that a rapidly 

 transpiring shoot possesses a consider- 

 able sucking-power arrange a shoot of 

 a sycamore, raspberry or sunflower as 

 in Fig. 87. 



Take a piece of rubber-tube (r) about 

 2 inches long and slip one end on the 

 end of the shoot, the other on a glass 

 tube (a). Firmly tie the rubber-titbe 

 to the shoot and the tube with string. 

 Allow the shoot to hang down, and 

 then pour water into the tube ; gently 

 tap the latter and squeeze the rubber- 

 tube so as to get rid of all air bubbles. 

 When the tube is full of water close 

 the end with the thumb, turn up the 

 apparatus into the position indicated in 

 the Fig. 87, and place the end of the 

 • tube below the water («) and mercury 

 (i) in the glass dish. Support the shoot 

 by means of the clip and expose the 

 Fig. 87. whole in a bright window. The water 



in the tube is transpired by the leaves of 

 the shoot, and a considerable amount of the mercury is lifted into the tube, 

 as shown at {*'). 



