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 . F 4 grms. 
Potassium nitrate. . 1 grm. 
Magnesium sulphate F 1s grm. 
Potassium acid phosphate . 1 germ. 
Potassium chloride . ; 0:5 grm. 
Ferric chloride solution . a few drops 
Water : ; : 7 ~~ litres 
12 
