AGRICULTURAL BOTANY 123 



filled with a mucilage-like substance called protoplasm, 

 and a thinner, more watery substance called cell sap. 

 As the end of the root pushes through the soil by growth, 

 new root hairs are formed in front of the older ones, 

 while those farthest back as rapidly die off, so that at 

 any given time only a short portion of a rootlet bears 

 hairs. A root hair never develops into a rootlet. 



It is usually difficult to see the root hairs of plants 

 growing in the ground, but with the help of a magnify- 

 ing glass they may be discovered if the particles of soil 

 about the younger roots are carefully removed. 



Suggestive Experiment. Place flax, clover, or timothy seed 

 on moist blotting paper. Keep the blotting paper between two plates to 

 prevent evaporation. Notice the velvety covering to the roots. These 

 are the root hairs above described. 



Uses of Root Hairs. Root hairs can take up water 

 freely, even from soil that does not appear very wet, 

 because each particle of soil, against which the hairs 

 lie very close, is surrounded by a thin layer, or film, of 

 water. Another thing of interest concerning root 

 hairs is that they are able, by means of an acid which 

 exudes from their tips, to aid in dissolving the mineral 

 matters in the soil which the plant needs for food. 



As the root hairs, then, aid in the work of solution 

 and do nearly all the work of absorption of the food the 

 plant obtains from the soil, it follows that the amount of 

 nourishment a given plant can receive from the ground 

 depends upon the number of the root tips, the only part 

 of the root which bears root hairs. 



Suggestive Experiment. On a small piece of polished 

 marble place some fine seed and keep the surface of the marble moist 

 under a cloth or blotting paper so that the seeds may germinate. As 



