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PLANT BIOLOGY 



Fig. 45. — Cross-section of Root, 



enlarged, showing root-hairs. 



cellular structure. The root-hair is a delicate tubular 

 cell (Fig. 45), within which is contained living matter 

 (protoplasm); and the protoplasmic lining membrane of the 



wall governs the entrance of 

 water and substances in solu- 

 tion. Being long and tube- 

 like, these root-hairs are 

 especially adapted for tak- 

 ing in the largest quantity 

 of solutions ; and they are 

 the principal means by which 

 plant-food is absorbed from 

 the soil, although the sur- 

 faces of the rootlets them- 

 selves do their part. Water 

 plants do not produce an 

 abundant system of root-hairs, and such plants depend 

 largely on their rootlets. 



The root-hairs are very small, often invisible. They, 

 with the young roots, are usually broken off when the 

 plant is pulled up. They are 

 best seen when seeds are germi- 

 nated between layers of dark 

 blotting paper or flannel. On 

 the young roots, they will be 

 seen as a mold-like or gossamer- 

 like covering. Root-hairs soon 

 die : they do not grow into roots. 

 New ones form as the root grows. 

 Osmosis. — The water with its 

 nourishment goes through the 

 thin walls of the root-hairs and rootlets by the process 

 of osmosis. If there are two liquids of different density 



Fig. 46. — Root-hair, much en- 

 larged, in contact with the soil 

 particles (s) . Air-spaces at a ; 

 water-films on the particles, as 

 at w. 



