Experiment III
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ffect of Nitrates upon Ratio of Tops to Roots in Corn Plants In order to get comparative data as to the effects of nitrates, ExperimentIII was conducted with corn. A selected variety of field corn was used.The method was practically the same as that used for barley. Three cornseedlings were employed to a culture and three cultures constituted a series.The first series was removed at the end of 27 days, the second at the endof 34 days, and the third at the end of 41 days. Both green and dry weightsof tops and roots are recorded, as are also the probable errors of the meansof the dry-weight ratios. It was found practicable in this experiment to usetwo solutions only, the low-nitrate and the medium-nitrate solutions. The results are given in table 6. The difference between the ratios oftops to roots is not significantly large for the first series; this was true alsoof the first series with barley, and indicates that the seedling is influencedmore greatly by the composition of the solutions after the tops have begunto function actively. The second series, however, gives a difference infavor of the medium-nitrate solution of 1.88 ± .261, and the third series adifference of 3.34 ± .678, as will be seen from the table. 432 AMERICAN JOURNAL OF BOTANY [Vol. 9, The increase in ratio of tops to roots as the plants grow older is broughtout in this experiment, as was the case for barley in Experiment I. Thus theresults of Experiment III confirm in every way those obtained with barley.The three experiments leave no doubt as to the effect of nitrates in increasingthe ratio of tops to roots in these two plants under the conditions employed. It is worthy of note, also, that there is little difference in the efficienciesof these two solutions as measured by total growth produced either in greenor in dry weight. (Green Wt.) (Dry Wt.) In Series 1, Sol. I, Total Growth 39.3199 3.8014 (low nitrate) Sol. II, " " 36.9930 3.2390 (medium nitrate) In Series 2, Sol. I, " " 49.4250 4.8440 Sol. II, " " 54.6613 4.4670 In Series 3, Sol. I, " " 61.4600 5.7998 Sol. II, " " 61.5000 5.5905 These figures show that plants in the higher-nitrate solution haverelatively higher water contents and correspondingly smaller dry weights.In the light of this fact, there is great need of more careful considerationthan is usually given as to what one desires of the plant before concludingas to the effectiveness of a particular solution or a particular fertilizer; also,dry-weight determinations which are not checked up occasionally withthe green weights may be wholly misleading as to the actual amount ofgrowth which may have taken place during a given period.
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