SCHREINER & SKINNER: EFFECT OF GUANIDIN ON PLANTS 537 
experiment. The solutions were analyzed for nitrates immediately 
after each change. The phosphate and potassium were deter- 
mined on a composite solution of the four changes. Observations 
on the general development of the plants and the effect on root 
growth and appearance were made during the experiment, and 
photographs were taken. 
For the purpose of preparing the 66 culture solutions needed 
in this investigation, stock solutions of the three salts, calcium 
acid phosphate, sodium nitrate, and potassium sulphate, were 
prepared separately. The salts were chemically pure salts and 
were dissolved in each case in physiologically pure water. For 
the calcium acid phosphate solution 1.776 grams of CaHy4(POx)s. 
H,O per liter were used. This solution has a concentration of 
1,000 parts per million of P.O;. The sodium nitrate solution was 
prepared by using 5,000 grams of NaNO; per liter. This solution 
is equivalent to a concentration of 1,000 parts per million of NHs. 
The potassium sulphate solution was prepared by dissolving 1.852 
grams of K,SQ, per liter. This solution has a concentration of 
1,000 parts per million of K,O. The amount of culture solution 
used in each culture bottle being 250 c.c., it follows that every 2 
c.c. of these 1,000 parts per million stock solutions will represent 
8 parts per million in the culture solution when this is diluted to 
the capacity of the bottle; i. e. the successive addition of 2 c.c. 
of the stock solution gives the 10 per cent differences desired in 
putting up the 66 solutions. In putting up the 66 cultures it was 
found desirable to calibrate each bottle for 250 c.c. capacity and 
to number them consecutively from 1 to 66. Bottles in which 
the 250 c.c. mark was either high or low were discarded, only 
those being used that brought the surface of the liquid from one- 
half to one centimeter from the top. These 66 bottles were then 
arranged in a triangular form, as illustrated by FIG. 1 and 2. 
The necessary amount of the 1,000 parts per million stock 
Solution above described was measured from a burette. For in- 
Stance, in adding the requisite amount of nitrate to the set of cul- 
ture bottles the line of bottles P to K in FIG. 2 received no nitrate 
Solution, the next line of bottles received 2 c.c. each, the third 
ine 4 c.c, each, and so on, increasing 2 c.c. with each successive 
line, the culture at N receiving 20 c.c. of the nitrate solution. 
