I.] NUTRITION OF THE PLANT 17 



making up the complete solution, thus obtaining media 

 for the plant containing no nitrogen, no phosphorus, no 

 potassium, etc., the other constituents found in the 

 plant being present in each case. The result of one 

 such series of experiments is shown in Fig. i, which 

 illustrates that when, e.g., nitrates are omitted from the 

 culture solution, the plant is quite unable to grow 

 after it has used up the material in the seed, however 

 freely it may have been provided with potassium, 

 magnesium, etc The net result of such experiments, 

 in agreement with the one shown in the photograph, 

 is that a plant must obtain by means of its root 

 nitrogen in combination, phosphorus, sulphur, potas- 

 sium, magnesium, calcium, and a little iron — all of 

 which constituents are indispensable to the growth 

 of the plant and cannot be omitted from the 

 culture solutions. Sodium, silicon, and probably chlo- 

 rine, though invariable constituents of the ash, are 

 not necessary and can be dispensed with. From 

 these water culture experiments we arrive, then, at 

 the conclusion that the plant must draw certain 

 elements, in quantities which are small compared 

 with the weight of the crop but are nevertheless 

 indispensable, out of the soil by means of its roots, the 

 rest of the plant being built up from air and water. 

 These water culture experiments may also be made 

 to lead to another conclusion, which we first of all 

 owe to de Saussure — that the nutrient substances 

 must first of all be dissolved or capable of going into 

 solution before they can feed the plant. The growing 

 plant contains 80 per cent, or more of water, but this 

 amount bears but a small proportion to the total 

 quantity of water which passes through the plant 

 during the whole period of growth. There exists, 

 in fact, a continual •' transpiration current " through 



