i88 
JOHN W. SHIVE AND WILLIAM H. MARTIN 
The solution giving the best growth of buckwheat tops contained 
the three salts in the following volume-molecular partial concentra- 
tions: KH2 PO4, 0.0108 m.; Ca(N03)2, 0.0130 m.; and MgS04, 0.0100 
m. This solution also produced the highest yield of roots. It will be 
observed that these proportions are not at all the same as are those 
which produced the maximum yield of buckwheat tops and of roots 
during the early period of growth, from germination to flowering. It 
thus appears that the salt proportions of the best physiologically 
balanced solutions for buckwheat during the early period of growth 
are totally different from those which characterize the best physiologi- 
cal balance for these plants during the later period, from flowering to • 
maturity. 
The optimal series of solutions with a total osmotic concentration 
value of 1 .75 atmospheres was repeated in sand cultures, with renewal 
of solutions as in the tests with solution cultures. The renewal of 
solutions in sand cultures was accomplished by a method similar to 
that employed by McCall.^ The containers, consisting of earthen- 
ware pots glazed inside and outside, each held 2,500 g. of washed, 
air-dry, white quartz sand. The sand in each pot was flooded with an 
initial application of 750 cc. of solution, the excess of which was then 
withdrawn, leaving the sand with a moisture content of approximately 
15 percent of the weight of the air-dry sand. The excess solution was 
withdrawn through a glass tube extending to the bottom of the pot, 
instead of through a metal tube sealed to the bottom of the pot, as 
was done by McCall. This method was found entirely satisfactory 
and prevented the possibility of any metal coming in contact with the 
solution. 
The first series of sand cultures was continued, with renewal of 
solutions (250 cc. of solution with each renewal) every three or four 
days, until the plants were in bloom. This required a time period of 
25 days after the seedlings were transferred to the sand cultures. The 
series was then repeated. These two series of sand cultures, one con- 
ducted in May and the other in June, corresponded to the two series 
of solution cultures conducted during the early period of growth, from 
germination to flowering. 
The solution in sand culture giving the highest yield of buckwheat 
tops during this early period of growth contained the three salts in the 
^ McCall, A. G. A new method for the study of plant nutrients in sand cultures. 
Amer. Soc. Agron. 7: 249-252. 1915. 
