SUITABLE PROJECTS IN PLANT CHEMISTRY It is suggested that experiments denling with the effects of gases on seedlings may seme as suituble project material, since definite results are obtainable within about ten days. Details of hno such experiments are given.
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At present many schools encourage their chemistry students to carry out special projects in place of a certain number of the regular experiments. It frequently happens that some students who are interested in plants express a desire to work on a project concerned with plant growth. Unfortunately, it is usually rather difficult to 6nd aplant project which will yield decisive results within the brief period ordinarily allotted to projects. The . writer has found that projects dealing with the effrcLs of gases on germinating seeds are well adapted to such short periods. .+project recently carried out here may s r n y to indicate the kind of results that can be obtained. After some mustard seeds had been soaked FIGURE 2 M U S T A R DSEEDLINGS A l T E R in water for several days they were 24 HOURS divided into two portions, one to be In oxygen, In air, kept in oxygen and the other in air as a control. The apparatus was arranged as in Figure 1. The water in the dish serves a double purpose; i t confines the gas inside the inverted jar ~
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and keeps the atmosphere sufficientlyhumid to prevent drying of the seeds. The procedure was quite simple. Every day a fresh jar of air or oxygen was inverted over the seeds, and after about twenty-four hours the changes were recorded. The results of the experiment can be read in the photographs. Figure 2 shows, to the right, the progress made during twenty-four hours' contact with oxygen. On the left are the controls which were exposed to ordinary air for the same length of time. Of 'those exposed to oxygen fifty-three had fbots, whereas only three of the controls had germinated. The roots on the latter were also smaller than those on the seeds kept in oxygen. The development resulting from forty-eight hours' exposure (Figures 3 and 4) needs little comment. In the
I'rcuna i . - h l u s m n ~ SEEDLINGS APTER 6 DAYS Top: In air. Bottom: I n oxygen.
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control group (Figure 3) the longest roots measure only inch, while those exposed t o oxygen attained a length of a/a inch, and in several cases more. In the latter moup - - we also found well-develo~edroot hairs. At the end of three days (Figures 5 and (i)the advantage of oxygen still continued to be quite evident. Leaves had made their appearance, and, although the fact does not show up distinctly in the illustrations, the seedlings reared in oxygen possessed well-developed leaf stems, whereas in the control group the stems barely extended beyond the seed. It may be of interest to note that the leaves possessed a rich green color as soon FIGURE9.-GERMINATING I'EAS AFTER 3 DAYS as they appeared. On account of A. In air. 0. In oxygen. overcrowding some of the seedlings were then weeded out, leaving typical representatives of each group. The good influence of starting in an atmosphere of oxygen continued in evidence a t the end of four days, but a t the end of five days the control group appeared to be catching up. At the end of six days (Figure 7) there were well-developed shoots in both groups. The advantage of an abundance of oxygen was no longer apparent. The food originally stored in the seeds was practically exhausted. I t must be remembered that some photosynthesis was possible in the seedlings kept in oxygen because a vaminz amount of , I-/carbon dioxide was present as or~ FIGURE 10.-GERMINATING PEASA m m 5 DAYS a r e ~ ~ i r a t by-product. Results of a similar experi4 . In air. 0. In oxygen. ment on peas are shown in the remaining photographs. Here, too, the seeds were first allowed to soak in water for a couple of days.
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Observations on Germinating Peas End of first day. (Figure 8.) In oxygen ( 0 ) : Average length of roots, '/a inch; one measured '/z inch. In air (A): One had failed to germinate; one root measured slightly over inch; others about ' / 4 inch.
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End of second day. (Not illustrated.) In oxygen: Leaves appearing on five seedlings. One root about 1'/16 inch long; others about 7/8 inch. Average thickness of roots greater than in controls. In air: Leaves appearing on one; one root just beginning to appear; longest root was one inch. Third day. (Figure 9.) In oxygen: Average length of roots about 11/4 inch. In air: Roots somewhat thimner than those in oxygen; longest root 13/16inch; shortest root inch. Fourth day. (Not illustrated.) In oxygen: Four roots, 13/4inches; two were ll/z inches; best stem, 3/r inch. In air: Three roots, inches each; one measured less than 3/1 inch. Fifth day. (Figure 10.) In oxygen: Sum of all root lengths, 12I/8 inches; combined lengths of shoots, 6 inches. In air: Combined root lengths, lZ1/, inches; combined stem lengths, 55//8inches. Sixth day. (Not illustrated.) In oxygen: Combined root lengths, 14l/r inches; combined lengths of shoots, 7 inches. In air: Combined root lengths, 1 4 v 8 inches; combined shoots, 7 inches. The foregoing experiments indicate that interesting results can be obtained within a week or ten days. It woufd be of interest to compare the response of a large variety of seeds. Other experiments will readily suggest themselves, such as the use of nitrous oxide in place of oxygen, mixtures of oxygen and carbon dioxide, carbon dioxide and air, etc. Since oxygen is a by-product of photosynthesis it might be of interest to determine whether the seedlings could survive in an atmosphere of pure carbon dioxide or in a mixture of carbon dioxide and nitrogen.
