Oct., 1922] TURNER EFFECTS OF CERTAIN MINERAL SALTS 
stages there is an increase in ratio of tops to roots as the nitrate content is 
increased. 
In addition to the unmistakable evidence given as to the effect of in- 
creasing the nitrate concentration in the solution, as a study of the probable 
errors of the differences will show, attention might be called again, in Series 
6, to the absolute dry weight of roots in the low-nitrate solution (1.8 131 
grams) and in the high-nitrate solution (1.1687 grams). The production 
of tops has been greatest in the medium-nitrate solution, as has been true 
throughout. If we now add total dry weights again for each of the three 
solutions, the interesting fact stands out that there is not a great difference 
in the total growth-producing value. The medium-nitrate solution is 
most efficient, with a total production of 13.2377 grams, followed by the 
high-nitrate solution with 11. 7 172 grams, and the low-nitrate solution with 
11.4555 grams. The two latter solutions have about the same total effi- 
ciency, yet the ratio of tops to roots is strikingly different, the difference of 
the means being 3.75 d= .238, or about 70 percent. 
Increase in Ratio of Tops to Roots as Plants Grow Older 
The ratio of tops to roots increased both with nitrate concentration of 
the solution and with increased age. The normal increase of this ratio 
with age has not been adequately considered heretofore in the literature, 
and as yet the exact mechanism underlying this phenomenon awaits ra- 
tional explanation. Table 4a gives data showing the increase with age; 
while the increases are quite significant in the low-nitrate solution, they are 
strikingly so in the medium- and high-nitrate solutions. 
Growth Features 
Quantitative data were not recorded as to transpiration or length of 
tops in Experiment I, but notes kept throughout the time the plants were 
growing show very little difference either in greenness or in height of tops. 
Plants grown in the low-nitrate solution were somewhat more slender, 
but appeared always more turgid. The aging or dying of the first or oldest 
leaf is not without interest. In the present experiment, as well as in the 
preliminary ones with barley, gradual dying of the lower leaf beginning 
with the tip started first with plants in the high-nitrate solution and would 
not begin in the low-nitrate solution until two or three weeks later. 
The longest roots occurred in the high-nitrate solution. These were 
less branched, and the root system appeared, therefore, more slender than 
those in the other two solutions. It was particularly noticeable that 
aerial roots were scarcely formed at all in the high-nitrate cultures, while 
they developed abundantly in the others. The less abundant production 
of lateral roots in the high-nitrate solution as found here is in contrast to 
Miiller-Thurgau's finding that the presence of nitrogen in a solution causes 
a much more vigorous grow^th of secondary roots. 
