OSMOSIS 



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water and the salts in solution pass into the cells of the root- 

 hairs and thence into the fibrous and tracheary tissues of the 

 root and thence through the same and probably other tissue of 

 the sap wood of the stem into the leaves where a considerable 

 part of it is given off by transpiration* (Chapter VIII.) The 

 exact process by which water passes through a growing plant is 



FIQ. 80. Apparatus for demonstrating osmosis; thistle tube on left and egg on right. 



not understood. Some of the acid within the root-hairs passes 

 out (exosmosis) and helps to dissolve the raw food compounds 

 in the soil, thus making them more available. If the character 

 of the soil is such that the water solution is of greater density 

 than the contents of the plant cells, the plant cannot live in it, 

 and if a plant should be set in such soil it would wilt very 

 quickly because of the loss of water which would pass out to 

 the soil. 

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