Potassium to Growth in Plants . 207 
It will be immediately noticed that in the buckwheat the roots are 
enormously richer in potassium than the tops. In the full nutritive solution 
the tops utilize only 0*53 grm. of potassium per gramme of dry matter formed 
against 1 grm. in the roots ; in the case of the nutritive solution less 
potassium the difference is even more marked : the tops utilize 0*15 grm. of 
potassium for every gramme of dry matter formed, while the roots consume 
1 grm. Japanese buckwheat behaves, therefore, in a manner wholly different 
from either wheat or corn, as regards potassium utilization per gramme of dry 
matter formed in tops and roots, but similarly to both these plants when we 
consider the potassium consumed by the plant as a whole per gramme of dry 
matter formed. In the case of wheat and corn the consumption per gramme 
of dry matter formed in the full nutritive solution is 0*0727 and 00688 grm., 
in the nutritive solution less potassium 0-0063 and 0-0067, while in the case of 
Japanese buckwheat these figures become 00593 g rm - an d 0-0089 grm. 
respectively. In the absence of potassium, buckwheat is apparently unable 
to effect as economic a utilization of the element as either wheat or corn, 
and further evidence in favour of this view will be found on p. 323. 
II. Effect of Delayed Additions of Potassium 
on Growth. 
In our experiments on the effect of delayed additions of potassium on 
growth we have used Blue stem Wheat, Early pedigree Dent field Corn, and 
Japanese buckwheat, all but one of the experiments being carried out in 
water culture. Some of the plants were grown in a full nutritive solution 
from the beginning, some in a solution free from potassium, while in the 
case of others potassium was usually added to the nutritive solution three, 
six, nine, and twelve days after the experiment was set up, though in one 
experiment with wheat the effect of additions delayed for longer periods 
was also tried. The nutritive solution (solution F) used was prepared as 
indicated in Table XII (see p. 201). Nutritive solution F has a concentra- 
tion greater than that of solution A and less than that of solution C by 
almost exactly half the difference between the two. The calcium-magne- 
sium ratio is 3-85 : i,i.e. slightly lower than that of solution A. Solution F 
contains more magnesium, calcium, and sulphur than solution A, but other- 
wise resembles it more closely than it does any of the other nutritive 
solutions used. As will be seen from the table, the potassium in solution F 
was added as the sulphate instead of the nitrate as in solution A. This was 
done so as to permit the use of the solution for the cultures less potassium, 
and for those which were to receive potassium after the lapse of specified 
times. The concentration of the solution in the absence of pof&ssium was 
2-4815 grm. per litre instead of 3*6635 grm. The plants growing throughout 
an experiment in the absence of potassium were therefore in a weaker 
