PASSAGE OF WATER THROUGH THE PLANT ll? 
The shoot remains fresh and the exposed wood 
~ 1s coloured red. 
The removing the outer tissue has not oe 
the passage of water through the plant, and as the 
wood is coloured red, it is clear that the water travels through 
the wood, Further, if the stem of the shoot is cut right 
across, it will be seen that the pith is not coloured. This 
shows that water travels through the wood alone and not 
through any other part of the stem. 
So far, then, we have seen that the water is taken in by the 
root-hairs ; owing chiefly to the physical process of diffusion, 
it travels from cell to cell through the wood of the stem of the 
plant, then through the leaf-stalk into the veins of the leaves. 
Result. 
Conclusion. 
The next series of experiments relate to the giving out of 
water by the leaves, a process known as Transpiration, which 
may be compared with the perspiration of animals. 
| Take some leaves of a shoot, the younger the 
better, and pass the leaf-stalks through holes in 
a piece of cardboard which rests on the top of a vessel con- 
taining water so that the leaf-stalks are in the water and the 
blades of the leaves resting on the cardboard. Cover over 
with a bell jar. 
Experiment I. 
Soon-the sides of the jar. become covered with 
drops of water. 
Conclusion. Leaves give off water. 
In order to see which side of the leaf gives off most water 
the test of cobalt paper may be applied. - 
Take a dry duster, which should first be 
warmed so that it may be. thoroughly dry. 
Lay it out flat, and on it place two ivy leaves, one with the 
under side uppermost, the other with the upper surface 
exposed. On these place cobalt paper, which, it is well known, 
changes from blue to red if exposed to damp. Cover with a 
sheet of glass.* 
Result 
Experiment II. 
**This is Darwin and Acton’s modification of Stahl’s Cobalt Method. 
See ‘Physiology of Plants,’ p. 105. 
9 
