Nature-Study Agriculture 



Osmosis 



Boot 

 pressure 



W. T. Skilling 



FIG. 7. Transpiration. These cans of earth were prepared in the same 

 manner and were balanced ; but the one with the growing crop (alfalfa) be- 

 came the lighter because of its greater loss of water. 



The process by which water, bearing its dissolved 

 food material from the soil, enters the roots may be 

 illustrated in various ways. One way is to use an egg 

 (Fig. 6) to represent the roots. (Exp. 5.) Without 

 breaking the white membrane within, pick off some of 

 the shell from the base of the egg and seal a small glass 

 tube into a small opening made through shell and mem- 

 brane at the point of the egg. (Tallow dropped from a 

 burning candle is good sealing material.) If this egg 

 is set in water, it will correspond to the roots standing 

 in soil moisture. The water will enter through the egg 

 membrane and push the contents of the shell up into 

 the glass tube. In the same way, water containing dis- 

 solved plant-food material enters the roots and pushes 



