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- 

 solve no more, the so- 

 lution has become very 



Fig. 39. — The 

 root-hairs of a rad- 

 ish seedling. 

 Through them the 

 plant feeds. 



heavy, and is 

 called saturated. Now let us see how 



Fig. 40. — A Test 



for Osmosis. 



A is the thistle- 

 tube, B the mem- 



brane, A' the heavier this attectS plants. 



solution, c the lighter T a k e what is called a 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 



