Potassium to Growth in Plants. 
223 
promptly exhibited, it will be noticed, in the ratios of top weight to root 
weight. The tops recover more promptly than do the roots. 
The distribution of potassium in the plants is shown in Table XXX. 
It will be noticed that the relative amount of potassium utilized by the 
tops and roots per gramme of dry matter formed is the same whether the 
potassium was added to the nutritive solution at the beginning of the 
experiment or only after twelve days, but that absence of potassium for the 
entire period of growth causes a marked change in the ratio to the 
advantage of the roots. In the absence of potassium, therefore, Japanese 
buckwheat does not behave like wheat and corn. It should, however, be 
noticed that in the case of wheat and corn the potassium requirements of the 
tops and roots per gramme of dry matter formed is substantially the same, 
whereas in the case of Japanese buckwheat the requirement of the roots is 
very nearly twice that of the tops. In other words, the roots of buckwheat 
require for normal development per gramme of dry matter formed twice as 
much potassium as the tops. In starvation, therefore, we would expect the 
roots of this plant to effect a less economical use of potassium than the tops, 
and the differences existing in the normal plant to be consequently exag- 
gerated in the starved plant, but that the normal ratio would be established 
upon the addition of potassium to the nutritive solution. This is exactly 
what happens, as the figures in Table XXXI will show. 
Table XXXI. Effect of potassium starvation on the amount of dry 
matter produced per gramme of potassium utilized in tops and roots 
of Japanese buckwheat. 
Nutritive solution used. Dr S matter formed per gramme of potassium 
Tops. 
Roots. 
Grm. 
Grm. 
Full nutritive solution 
17.7 
9.4 
Nutritive solution plus potassium after 3 days 
16.7 
10-9 
>, „ 6 „ 
17.8 
II- 5 
}> }} 9 >> 
T 9-4 
12.7 
}} >? 12 
20-6 
13.0 
Nutritive solution less potassium 
159.2 
24.7 
A study of Table XXX will further show that, as was found in the case 
of corn, the potassium utilized per gramme of dry matter formed is slightly 
higher when the element is only added to the nutritive solution on the third 
day. In the case of corn a slight increase in dry weight was at the same 
time recorded, but in the case of Japanese buckwheat a loss of weight was 
obtained of about the same magnitude. This behaviour indicates that the 
potassium content of the seed does not primarily determine the length of 
time potassium may be withheld without causing loss of weight. A plant 
grown from Blue stem Wheat seed, which contains o*i i mg. of potassium, was 
unable to recover when this element was withheld three days, but a plant of 
