PLANT PH78I0L00T. 



75 



however, that solutions are not always absorbed without 

 modification; thus, of a 2-per- 

 cent solution outside of the cell 

 proportionately more water than 

 dissolved substance may be ab- 

 sorbed, so that the solution in 

 the cell may have a strength of 

 no more than 1 per cent; or the 

 opposite may occur, and the 

 strength of the solution in the 

 cell may be greater than that out- 

 side of it. This selective power 

 may even bring about chemical 

 changes in the watery solutions, 

 when the plant-cells absorb cer- 

 tain constituent parts of the 

 chemical compounds. In simple 

 plants all parts of the plant-body 

 absorb from the surrounding y^^^iti^^t&A^'^^^l 

 water equally, and this appears LiJI'^orwh^t.^x «io.°*(AftCT 

 to be the case with all true 



aquatics. In terrestrial plants, however, the absorption 

 of watery solutions is almost or entirely confined to the 

 parts in the ground (hairs or roots Fig. 46). 



129. Plant-food. — The most important elements which 

 are used in the nutrition of plants, or which, in other 

 words, enter into their food, are Carbon, Hydrogen, Oxy- 

 gen, Nitrogen, Sulphur, Iron, and Potassium. These all 

 appear to be necessary to the life and growth of the plant, 

 and if any of them are wanting in the water, soil, or air 

 from which the plant derives its nourishment, death from 

 starvation will soon follow. 



