1920] 
DUGGAR—INSOLUBLE SALTS IN BALANCED SOLUTIONS 309 
be possible to effect a circulation of fresh nutrient solutions 
where soluble salts are employed, but any operation of this 
nature would be impracticable in most of our experimental 
work. After all, the problem is to obtain a combination of 
salts favorable to a high degree which may be employed in 
practically any type of experiment where the desire is to main- 
tain the plant under satisfactory physiological conditions. If 
the labor involved is great in the one case and small in the other 
the one involving the less labor will, of course, be selected as 
the more practicable. 
Before describing in detail the methods and experiments to 
be discussed it should be pointed out that the nutrient solution 
developed by Crone (703) and considered by him to have certain 
advantages over the Pfeffer solution, contained, in addition to 
KNO,, MgSO., and CaSO,, ferrous phosphate and tribasic cal- 
cium phosphate. The two salts last mentioned are, of course, 
relatively insoluble and were used by Crone with the idea of 
diminishing the chlorosis which he attributed to the excess of 
soluble phosphate and the low content of iron. Later, how- 
ever, Benecke ('09) was unable to substantiate the claims made 
by Crone as to the benefits to be derived from the type of solu- 
tion which the latter had formulated. 
The experiments on which the data in table 1 are based were 
carried out in the experimental greenhouse at the Missouri Bo- 
tanical Garden during April, 1920. The methods employed were 
in fairly close accord with those previously described. Glass 
tumblers of 250 cc. capacity were used with 240 cc. of nutrient 
solution. To these containers were fitted corks 7.5 em. in diam- 
eter and 0.7 cm. in thickness, arranged with holes for the inser- 
tion of the roots of the seedlings, and with an extra hole to facili- 
tate the addition of water lost by transpiration. The seedlings 
were germinated over water, and in order to insure the greatest 
possible uniformity in size a selection of these was made when 
the shoots were about 2 cm. in height. Each cork was held in 
position by a stout rubber band passing around the tumbler 
lengthwise. The tumblers were covered as usual to protect the 
roots from the light, and the cultures were then freely and equally 
exposed on a lattice bench in the greenhouse. The variety of 
wheat employed throughout was the Pacific Coast Blue Stem, 
