THE CONSTITUENTS OF THE ASH OF PLANTS 177 



performance of one or more of them under the influence of 

 disturbance of quantitative relations may obscure the action 

 of any element, or group of elements, in whatever combina- 

 tion it or they may be existing. Probably all the essential 

 elements of the ash play many parts, all co-ordinated by 

 the living substance of the organism. Whether any of the 

 constituents of the ash actually enter into the composition 

 of protoplasm is doubtful, but several of them appear to 

 be necessary for the assimilation of the food which is either 

 manufactured or supplied, as well in the case of the vegetable 

 as in that of the animal organism. 



From the nature of the plant-body and the absence of the 

 localisation of different functions in particular organs which 

 is so much more clearly characteristic of the animal organism, 

 it becomes very difficult to ascertain the exact nature of any 

 part played by any of these ash constituents. We can more 

 easily determine what is the effect produced by variations in 

 the amount supplied or by the total absence of any of them. 

 This effect is usually, however, only the general effect upon 

 the plant, and the experiments leave us still quite in the 

 dark as to the way in which any general effect is produced, 

 whether directly or indirectly by affecting the health of the 

 plant and thus leading to secondary changes in its tissues. 



The experiments in question are preferably carried out 

 by means of water-culture, the general nature of which wet 

 have already explained. Plants will grow very well in 

 water containing small quantities of various inorganic salts, 

 and these can be varied at will for the purpose of definite 

 inquiries. The composition of such a culture-solution is 

 given by Pfeffer as under : 



Calcium nitrate . . 4 grms. 



Potassium nitrate . . 1 grm. 



Magnesium sulphate . 1 grm. 



Potassium acid phosphate . 1 grm. 



Potassium chloride . . 0-5 grm. 



Ferric chloride solution . a few drops 



Water ... 7 litres 



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