WATER- ABSORPTION AND TRANSPIRATION. 



123 



suck fresh supplies upwards to replace that removed by the 

 air in the form of water- vapour, and in tl e second place the 

 root may exercise a pushing force (root-pressure), driving 

 water upwards. Experiments with leaves or shoots cut off 

 and set in water prove that the leaves draw water upwards. 

 How can we find out whether water is forced upwards by the 

 root? See Art. 159, however. 



* (a) Choose a healthy Bean seedling growing in soil in a pot, and cut 

 across its stem about 3 ins. above the soil. Tie a bit of stout rubber 

 tubing, a few inches long, on 

 the stump, and fill this tube 

 with water, then tie into the 

 rubber tube a glass tube of fine 

 bore (capillary tubing). Sup- 

 port the glass tube horizon- 

 tally by means of a cleft 

 stick ; squeeze the rubber tube 

 so as to force some water out 

 of the end of the glass tube 

 and absorb it with blotting- 

 paper, then release the rubber 

 tube so that air is drawn into 

 the glass tube. Watch the 

 advance of the water (which 

 should be coloured with red 

 ink) along the glass tube. Try 

 this experiment with vigorous 

 plants of various kinds grow- 

 ing in pots. 



(6) Cut off the stem close to 

 the ground, and connect the 

 stump to a long, straight piece 

 of glass tubing ; lash this tube 

 to a stick placed in the soil, 

 pour a little water into it, 

 then a drop of oil, which will 

 float on the water and pre- 

 vent evaporation. Measure the ascent of the water in the tube, and 

 find out how the rate is affected by temperature. 



rtOOT-HAIRS 5 



Fig. 45. Mustard Seedlings grown in Sand 

 (a has been gently shaken in water). 



157. Root-Hairs are developed on roots a short distance 

 behind the root-cap. They soon die away from the older parts 

 of the root. They come into very close contact with the 

 earthy particles, so that when the root of a seedling is 

 lifted from the soil a portion of the latter adheres wherever 

 root-hairs are present (Fig. 45), but not where they are absent. 



