THE LIFE OF A PLANT 



67 



to use a magnifier in order to see these root-hairs. They are 

 the parts which do the work of drinking in the water. 



But if we suppose they have mouths for this drinking, we 

 are mistaken. Their walls may be very thin, but they have 

 no openings. How can water go through 

 the root-skin, or membrane? 



Let us first understand what is meant 

 by a solution. It is water in which some- 

 thing has been dissolved. Stir salt in water, 

 and we have a solution of salt. Touch the 

 tongue to it, and we taste the salt. It is 



by dissolving the salt that 



we taste it, for if we 



should put dry salt on 



a perfectly dry tongue 



we could not taste it. 

 Second, some solutions 



are thicker, or heavier, 



or denser than others. 



Salt and water is heavier 



than water alone, and 



white of egg is heavier 



still. If we keep on ad- 

 ding salt to our solution 



until the water can dis- 

 TEST solve no more, the so- 

 lution has become very heavy, and is 



FIG. 39. The 

 root-hairs of a rad- 

 ish seedling. 

 Through them the 

 plant feeds. 



let us see how 



FIG. 40. A 

 FOR OSMOSIS. 



A is the thistle- called saturated. Now 



tube, .D the mem- 

 brane, A ' the heavier this affects plants. 



solution^ the lighter Take what ig called & thistle-tube, and 



over its large end tie a membrane of some 



kind. A piece of bladder is usually to be had for this 



purpose. Take also a wide-mouthed jar partly filled with 



