Apr. 19,1924 Orange Trees and Nutrient Solution Concentrations 
281 
of culture solution, but the ratio of the total dry weight of leaves and shoots to 
that of rootlets increased with increasing concentrations of culture solution. 
The increased nitrate content of the more concentrated solutions may play an 
important part in determining the ratio of tops to roots. 
Photographs were taken of the trees just prior to their removal from the con¬ 
tainers, nearly 21 months after the trees were planted. Plate 1, A, B, and C, 
shows the condition of the trees receiving different solutions, and D shows their 
root systems. 
The per cent of ash (Table V) in the various portions of the trees is greatest in 
those trees receiving the double strength solution. The percentages of ash in the 
rootlets show the largest differences, the per cent of ash in the rootlets of the 
trees receiving double strength solution being about twice that of the rootlets 
receiving quarter or half strength solutions. The composition of the ash of 
the three series of trees was not materially different except in the case of P0 4 , 
The percentages of each cation in the leaves, shoots, trunk, and root are approxi¬ 
mately constant for the different concentrations of culture solution. The per¬ 
centage of sodium in the ash of the rootlets increases with increasing concentra¬ 
tion of the culture solution, while that of potassium is approximately constant 
at the two lower concentrations of culture solution, but is higher in the ash of 
the rootlets at the highest concentration. 
Table V shows that in general there is very little change in percentage com¬ 
position with increasing concentration of culture solution. The trees apparently 
utilized the increase of nutrient ions in large measure for increases in size instead 
of producing a given amount of growth and accumulating large concentrations 
of certain ions, as frequently happens when trees are grown in unfavorable 
culture solutions. 
THE EFFECT OF CONCENTRATION UPON THE SOLUBILITY OF 
INORGANIC CONSTITUENTS OF THE DRY MATTER OF THE 
TREES 
Table V contains data showing the soluble fraction of the constituents deter¬ 
mined in the dry matter of all portions of these trees. The fraction dissolved in 
water was greatest in the rootlets, and least in the trunk. There was a tendency 
toward increased solubility in the ash as the concentration of the nutrient solu¬ 
tions was increased. Taking a general view of the data presented in Table V, 
it appears that an increased concentration of salts in the nutrient solution results 
not only in an increased concentration of ions in the ash of the trees which re¬ 
ceived them, but in an increase of the fraction which is soluble in water. The 
case of calcium forms a conspicuous exception to the statement just made. This 
accumulation of surplus materials in a soluble state should set aside certain as¬ 
sumptions on the principles of absorption by plants which postulate insolubility 
instead of solubility ( 6 ). Moreover, the discovery of this condition in orange 
trees explains certain effects which have been observed in soils of high salt 
content. We should especially like to emphasize the importance of the cal¬ 
cium relation. Previous papers by the writers (4 and 5) have contained 
data on the harmful effects of sodium salts and on the ameliorating effects 
of calcium salts upon orange trees. Now, if the solubility relations are main¬ 
tained as concentrations increase, it is apparent that as the concentration of the 
harmful sodium salts increases in the trees their relative solubility increases, 
while as the concentration of the beneficial calcium ion increases its relative 
solubility decreases, except in the leaves. If this be the case, we are then in a 
better position to understand the results often observed when trees grow in soils 
of high salt content. 
