SALT REQUIREMENT FOR BUCKWHEAT PLANTS 1 89 
same volume-molecular partial concentrations as did the solution 
giving the highest dry weight of tops and of roots in the corresponding 
series of water cultures. In the solution of the sand culture which gave 
the highest dry weight of roots^ the volume-molecular partial concen- 
trations were not the same as were those in the solution giving the 
highest dry weight of tops. The volume-molecular proportions of the 
three salts which gave the highest yield of roots were: KH2PO4, 
0.0180 m.; Ca(N03)2, 0.0104 m.; MgS04, 0.0050 m. 
To determine the salt proportions required to produce approxi- 
mately optimum growth of buckwheat in sand cultures during the 
period between flowering and maturity, the following procedure was 
adopted: The plants were first grown to the flowering stage in sand 
cultures, all of which contained the same solution. This solution had 
the salt proportions giving the best growth of tops in sand culture and 
in water culture during the early period of growth, from germination 
to flowering. The solutions were renewed every three or four days. 
At the end of this early 25-day period the cultures were all nearly 
alike, the plants throughout showing exceptional uniformity. 
The solutions in the sand cultures were now replaced by the 36 
different solutions of the optimal three-salt series. This was accom- 
plished by passing through the sand of each culture (after first adding 
sufficient distilled water to bring the entire system back to its original 
weight) a triple portion (750 cc.) of the new solution, thus flushing out 
the old solution and replacing it with the new. At the same time the 
solution of one culture was replaced with Knop's solution, and that of 
another with Tottingham's best solution for wheat, each with a total 
osmotic concentration value of 1.75 atmospheres. 
The series was now conducted, with renewal of solutions as before, 
until the seeds were mature. This second growth period extended 
over a time interval of 30 days. The series was then repeated. The 
first of these two series was conducted from April 25 to June 19. 
The second series, which was just Hke the first, was carried out between 
July 2 and August 27. 
The highest yield of tops, of roots, and of seeds, was obtained from 
the same culture. The solution of this culture contained the three 
salts in the same volume-molecular partial concentrations as did the 
^ The dry weights of roots from the sand cultures were obtained by a method 
similar to that employed by McCall, Physiological balance of nutrient solutions for 
plants in sand cultures. Soil Science 2: 207-253. 1916. 
