xi ABSORPTION AND MOVEMENT OF WATER 145 



the atmosphere. They were said to be drops of dew. But in 

 far the larger number of cases the water has been pumped out 

 of the water-pores. The roots have taken in an excess of water, 

 which has been forced up the stem to the leaves. In these 

 plants transpiration is reduced to a minimum, and the water 

 exudes from the water pores, stomata, or through the epidermis. 

 These drops are evaporated as the sun gains more and more 

 power. A deposit of carbonate of lime, or some other mineral 

 which encrusts the leaves, is often left behind, as in the London 

 Pride, Gooseberry, and Currant. 



EXPT. 135. Examine a leaf of the Lady's Mantle on a warm summer 

 morning. Note 



(i) The leaf forms a little cup, and is shaped like a mantle with a 

 number of lobes. 



(ii) The cup of the leaf is often filled with water which has oozed out 

 of every leaf-tooth. 



(iii) That after emptying the leaf, drops of water ooze out of the end 

 of the leaf-teeth and collect in the bottom of the leaf. 



EXPT. 136. Examine the leaves of the Arum, also known as the 

 Cuckoo-pint, or Lords and Ladies. 



(i) The leaves are very long (from 6 to 10 inches), and are hastate- 

 cordate in shape. 



(ii) Drops of water can be seen to fall from the tips of the larger 

 leaves at very short intervals. 



EXPT. 137. Place a bell-jar over some grass plants which are grow- 

 ing actively. Note 



(i) The leaves, which were dry to commence with, become in a short 

 time covered with drops of moisture. 



(ii) Remove the bell-jar, and the moisture evaporates into the 

 atmosphere. 



Root-Pressure. If the stem of a vigorously-growing plant, 

 such as the Indian Corn or Sunflower, be cut off just above the 

 soil, and the cut surface be dried and examined by a hand lens, 

 water is seen to ooze out of the cut vascular bundles. It is also 

 a well-known fact, that if a vine is cut in spring, the cut stem 

 will bleed ; but if it is cut in summer, when the foliage leaves are 

 fully developed and transpiring, it will not bleed. The power 

 which the roots possess of forcing water up the stem is called 

 root-pressure. 



The amount of this pressure can be measured by cutting off 

 the Gtem of a plant just above the surface of the ground, and 



L 



