Journal of Agricultural Research 
Vol. XXVII, No. 2 
1 16 
brought about by a soil moisture content which tends to be too low or 
too high for unrestricted growth, or, in the case of water cultures, by 
great dilution of the solution. 
An examination of Tables II and IV shows, first as regards the yield 
of tops and grain obtained from the various nutrient treatments, that 
only cultures 00 , OB, IA, and IVB have produced yields comparable 
to ordinary yields of field-grown plants—i. e., above 15 bushels per acre. 
Culture 00 is similar to Shive’s R 3 C 3 which was found most suitable 
for growth of wheat seedlings during the first 30 days. It is to be 
noted that in yield of grain this culture was exceeded only by IVB 
containing CaCl 2 . Even the addition of nitrate, an ion which Hoag- 
land (jo) has shown may be absorbed very rapidly from solutions and 
which may therefore be deficient, particularly during the period of 
greatest absorption, in sand or solution cultures carried on as these 
were, resulted only in increasing the yield of tops. The reason for the 
striking increase in grain produced by the addition of CaCl 2 to the 
Shive solution is not clear. It can hardly be attributed to the direct 
nutritive value of calcium, but is more likely to be accounted for either 
by an improvement in the reaction of the culture medium or by render¬ 
ing other ions “physiologically available” (True, ( 21 )). A depressing 
effect on plant growth resulting from too high acidity of the medium 
has been observed by a number of recent investigators, and it has been 
shown that a correlation exists between acidity of the cell sap and 
retarded growth ( 20 ). Whatever the explanation, it is significant in 
this case that the Shive solution, modified by the addition of 0.0171 
gram molecules of CaCl 2 per liter, has produced a growth of mature 
wheat that in respect to yield and water requirement is comparable 
to that of plants grown under the best pot culture methods that 
have been devised or with that of field-grown wheat. The low-water 
requirements shown by these plants, both for tops and for grain, is in 
line with expectations if one of the functions of calcium, as stated by 
True ( 21 ), is to maintain normal permeability relations of the cell wall. 
As regards the effect of mineral nutrition on the development of rust, 
it appears that the application of an excess of nitrate has resulted in 
greater susceptibility to rust in both the leaf-rust and stem-rust series. 
In Culture IA, where the additional nitrogen did not so greatly delay 
maturity, the infected plants show a much reduced yield of grain also. 
The appearance of the plants themselves, particularly in the leaf-rust 
set, confirmed their more ready susceptibility, as both the number and 
size of pustules were greater on plants receiving additional nitrogen. 
The more luxuriant development of culms and the more rapid growth of 
these plants seem sufficient to account for the greater development of 
rust, and until further evidence is at hand, the assumption of a physio¬ 
logically greater susceptibility to rust in nitrogen-fertilized plants is 
unnecessary. 
The slight development of rast on the plants receiving calcium and 
magnesium is noteworthy since in these cultures the effect can not be 
attributed to generally poor growth, which is the case in those fertilized 
with phosphate and potash. It appears that the plants of Cultures IV 
and V actually were somewhat physiologically resistant, since repeated 
attempts to infect them were only partially successful. Hurd 6 indicates 
6 Hurd, Annie M., The acidity op some rust and smut resistant and susceptible varieties 
op wheat and some Pactors affecting it. Abstract presented at the meetings of the Physiological 
Section, American Bot. Soe., at Toronto, Canada, Dec. 39, 1931. (Mimeographed.) 
