140 Education through Nature 



small opening into which insert a small glass tube and 

 fix with sealing wax; allow to stand for twenty-four 

 to forty-eight hours. The contents of the egg has 

 risen to the top of the tube and flows out. Osmosis 

 through animal membrane. Explain the result. 



In a similar way roots and root hairs take in water 

 and dissolved substances from the soil and cause it to 

 rise in the stem of the plant. 



The last experiment is a clear case of pressure 

 caused by osmosis. The experiment with the filter 

 paper is an illustration of the effects of capillary attrac- 

 tion. Both of these forces are active in plants, causing 

 the flow of sap. Evaporation from the leaves of the 

 plant increases the rapidity of the upward current; 

 just as the exposure of the strip of filter-paper to dry 

 air increases the loss of water from the bottle. 



IX. On Transpiration, (a) Invert a dry tumbler 

 over a bunch of fresh white clover; observe the cloudy 

 appearance on the glass, due to transpiration, (b) 

 Wind a piece of sheet rubber tightly around one finger. 

 Note the moist skin on removing the rubber perspira- 

 tion, (c) Take two bottles; fill one with water. Place 

 into the bottle a few short branches or stems of white 

 clover bearing leaves. Some also into the empty 

 bottle. After a day or two note the difference. Why 

 does the water in one bottle prevent the wilting of the 

 plant ? 



X. How Excessive Transpiration is Regulated. 

 Take two potatoes of unequal size; peel off the out- 

 side of the larger one till its weight is equal to that of 

 the smaller one. Expose both to the air for a week 

 or so. Which is now the heavier ? How was evapora> 

 tion and drying prevented in the unpeeled potato ? 



Why are plants and animals covered with an outer 

 cuticle? Corks are made from bark; put one into 

 water; does it become soaked? Of what use is bark 

 on stems when absent from leaves? 



