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B. E. LIVINGSTON. AND W. E. TOTTINGHAM 
in but one of the three controls. It appears that some evidences of 
poisoning may be expected whenever maximum dry-weight values are 
obtained with young wheat plants,^ if the transpiration rate is not too 
low. Our best culture without magnesium poisoning was with solution 
R8C1, and this solution appears to be about as efficient as R6C1 on 
the basis of the growth data of table 2. As might be expected, the 
greatest water-absorption (transpiration) occurred with solution 
R8C1, where leaf injury was not manifest, but the difference between 
R8C1 and R6C1 is not great. In regard to the dry yield of tops, 
solutions R6C1 and R8C1 appear to be equivalent from the rounded- 
up data of the table, but there is actually a slight (though insignificant) 
difference between them, in favor of the former. 
Another form of injury, consisting of a withering and darkening 
of the leaf backward from the tip, occurred in certain cultures that 
were free from magnesium injury (see those marked % and § in the fourth 
column of table 2). It is suggested that this is due to too high acidity 
of the solution, and it may be tentatively called "acid" injury, until 
the relations of hydrogen-ion concentration are studied in such series 
as these. No acid injury was manifest with either solution R6C1 or 
R8C1, nor was it observed in any of the controls. 
Summarizing the results of this preliminary study, it appears that 
the numerical criteria that we employed indicate that our solution 
R6C1 is as good as (or slightly better than) Shive's optimal solution 
R5C2. Both these solutions induce some magnesium injury in young 
wheat plants, however. Considering the occurrence of this injury and 
the criterion of water absorption, as well as the production of dry yield, 
the best balanced solution (for these plants) of our entire series is 
R8C1, which contains, per liter, 0.0288 g.-mol. of KN0,3, 0.0026 
g.-mol. of Ca(H2P04)2, and 0.0050 g.-mol. of MgS04. This solution 
appears to be better suited to give maximum growth combined with 
perfect health of plants than does either one of the two other solu- 
tions just mentioned. Judging from all the evidence at hand (including 
^ This point was first emphasized by Free and Trelease, who remark: "It may 
be a general rule that increased growth is the first response to agents or circumstances 
which would prove injuriously toxic in greater concentration or on longer exposure. 
. In other words, slight poisoning, such as that caused by magnesium or boron, 
is essential for the production of the greatest dry weight of tops. Either magnesium 
or boron will serve." See: Free, E. E., and Trelease, S. F, The effects of certain 
mineral poisons on young wheat plants in three-salt nutrient solutions. Johns 
Hopkins Univ. Circ. March, 191 7, pp. 199-201. 
