536 SCHREINER & SKINNER: EFFECT OF GUANIDIN ON PLANTS 
thoroughly studied, and in this later work nutrient culture solu- 
tions, 66 in number, have been used, comprising all the combina- 
tions of potash, phosphate, and nitrate, as explained below. 
EXPERIMENTAL METHODS 
Wheat seedlings were grown in aqueous culture solutions con- 
taining the ordinary fertilizer salts, calcium acid phosphate, 
sodium nitrate, and potassium sulphate. Some of the cultures 
contained calcium acid phosphate only, some sodium nitrate only, 
and some potassium sulphate only. Other solutions were com- 
posed of mixtures of two salts, sodium nitrate and calcium acid 
phosphate, sodium nitrate and potassium sulphate, and calcium 
acid phosphate and potassium sulphate. Still other solutions 
had all three constituents in various proportions. The concentra- 
tion of all the solutions was 80 parts per million of the fertilizer 
ingredients, P2Os, NH3, and K,O. In cultures containing only one 
fertilizer salt, for instance calcium acid phosphate, the concentra- 
tion was 80 parts per million of P2Os. If two salts were present, 
for instance calcium acid phosphate and sodium nitrate, the 
concentration was 80 parts per million of POs + NH. If all 
three salts were present, the concentration was 80 parts per million 
of P.O; + NH; + KO. The ratios of the constituents varied in 
10 per cent stages. In all, there were 66 different cultures of 
nutrient solutions. ; 
For a more detailed explanation of this triangular scheme and 
the principles involved in preparing culture solutions in definite 
progression of its constituents, the reader is referred to earlier 
publications.* 
Two sets of cultures were prepared; to one set was added 
merely the nutrient salts, while to each culture of a similar - 
guanidin carbonate was added in amounts of 25 parts per million 
in addition to the nutrient salts. The culture solutions were con- 
tained in wide-mouth bottles, holding 250 c.c., and 10 wheat seed- 
lings grown in each culture. The culture solutions were changed 
every three days, four changes being made in the course of US 
* Schreiner, O., and Skinner, J. J. Some effects of a harmful organic ae 
stituent. U.S. Dept. Agr. Bur. Soils Bull. 70. 1910. Ratio of phosphate, 
and potassium on absorption and growth. Bot. Gaz. 50: I. 1910. 
