The subject may be, however, further elucidated by referring to some of these. Dr. Draper,. in his elaborate investigation of the forces which exert a controlling influence on the growth of plants, records a series of experiments on peas. He placed them just after they begun to grow in blue, red, and yellow light, and also in the dark, and in the open air. His observations were confined to the third and fourteenth days. At the former period he found that under the red the plant had attained 4.5 times its original size, and had produced double the number of leaves; under the blue, three times its original height, with also double the number of leaves. In the dark there was about the same increase of altitude, while in the open air only twice the original height had been attained, and there were no fresh leaves; and under the yellow light, a still smaller advance had been made. On the fourteenth day he found all his pea-plants green, though varying a little in the character of the color, except those which had been placed in the dark, which were of a pale whitish yellow, the plants vigorous, thirteen times their original height, but with no fresh leaves. On the whole, then, as far as Dr. Draper's experiment goes, it is in accordance with my results.

M. Senebier describes an experiment performed by him on lettuce-seeds sown in little cups and placed respectively in the open air in full light of day, in darkness, and under glass vessels filled with colorless, yellow, red, and violet fluids. "Observing then the effects produced by the different portions of light which were thus permitted to act, he found that the plants illuminated by the yellow rays grew most rapidly in height; next, those in the violet rays; afterwards those in the red rays. The plants which grew in light transmitted through water were still smaller and approached in size to those which flourished in the open air, while those in perfect darkness attained the greatest height of all. These last plants perished on the eighth day, and those in the yellow light on the ninth day, while all the others continued to vegetate. At the end of about five weeks, the plants growing under the red vessel were 4 inches and 9 lines in height; under the violet vessel 3 inches and 3 lines; under the water vessel 2 inches and 10 lines, and 1 inch and 3 lines in the open air. With respect to the general appearance of the plants, the leaves of those which grew in red light were smaller and less smooth than those of the plants in violet light, or than the leaves of the plants confined under water, or than the leaves of those which grew in the open air. As to color, the leaves exposed to yellow light were at first green and afterwards became yellow; those in red light appeared green and preserved a tinge of that color; those in violet light were quite green and their color augmented with their age; while those raised in obscurity possessed no verdure at all." These experiments were repeated on French

beans with nearly similar results, but beyond the observation that "in proportion as the plants grew in height, in different kinds of light, the number and size of their leaves diminished," his attention appears to have been directed only to the question of color.*

Besides the experiments already detailed in this Report, and those on wheat and Malope trifida described in my former one, I have a few other observations on the effect of various qualities of light on the growth of plants from the seed, which it may be worth while briefly to record. They were made on the Collinsia bicolor of the florists, and Mignonette.

Seeds of the Collinsia were sown in garden mould in glasses, and placed under the colorless, blue, yellow, red, and darkened shades, on a table before a window which had a northwest aspect. The perforated boards were used for supporting the glass covers. The experiment was commenced on the 6th of July in last year. On the 9th it was found that germination had taken place under each glass except the yellow, where no plant grew until the 14th. Under the colorless glass, the plants grew and flourished till the beginning of August, when they all faded and died. Under the blue and red glasses they grew well for a while, but began to droop by the 26th of July. Those under the darkened glass existed rather longer, but they were tall and scraggy, and the leaves did not fairly open. Only three plants germinated under the yellow shade; they were all unhealthy and died before the 26th. On August 4th, seeds were sown afresh under each glass. Much the same order of growth was observed.

On October 12th, a hundred seeds of Mignonette were sown in each of seven glasses filled with garden mould. They were placed about a third of an inch below the surface. Six of the glasses were covered respectively with the colorless, blue, red, yellow, obscured colorless, and obscured yellow shades, and the seventh was placed in a dark closet. It should be observed that the closet was rather warmer than the room. The Mignonette seeds began first to germinate in the dark, then under the blue; then, after the lapse of a few days, they appeared under the red, and colorless, and the obscured colorless glasses. The yellow ray long retarded, and very nearly prevented their germination. Those in the dark were tall, thin, and yellow; they all died about November 1st; the others soon followed, excepting one plant under the colorless glass, which was found still alive with four green leaves on December 10th.

The investigations of many experimenters have shown that oxygen is necessary in the germination of seeds. The explanation given is that that element is required for instituting the action that converts the fecula of the cotyledon into sugar. It

* From Ellis's "Farther Inquiries," &c.

is unquestionable, that in the majority of cases, plants after the first stage of their growth require a certain supply of carbonic acid, by the decomposition of which they obtain carbon, setting free oxygen. My brother and I have shown that plants will exist well for a considerable time in an atmosphere devoid of oxygen, for instance in nitrogen, hydrogen, coal-gas, or carbonic oxyd. In order to see the effects of all these atmospheric conditions on the germination of wheat and peas, the following experi ments were made during the latter part of May and the beginning of June.

Six wheat-seeds and six peas were placed on folds of linen. floating on mercury, and covered with a colorless glass jar having a capacity of about 20 cubic inches. The linen preserved the seeds from the mercury, and was kept wet by the introduction of a small quantity of water. The jar was full of atmospheric air, and was placed on the table before the window having a SE aspect. After a couple of days or so the peas germinated, and shortly afterwards the wheat. They grew for about a week, and retained a healthy appearance much longer. The experiment was twice performed with similar results, and showed that the arrangement was applicable to the proposed experiments.

A precisely similar arrangement was made in a jar containing 29 cubic inches of hydrogen gas, and having in it a tube containing pyrogallate of potash, so as to absorb any trace of oxygen which might be accidentally present in the gas, or might be evolved from the seeds themselves. In four days the swollen peas had begun to burst. They put forth short radicles, but no plume, and in about a week afterwards they were all decaying. The wheat showed no appearance whatever of germination. This experiment was twice performed with the same result.

Another such arrangement was made in a jar filled with carbonic acid. Not the slightest appearance was indicated by either the wheat or the peas. They decayed, becoming soft and swollen, and emitted a most offensive smell on the removal of the jar.

The same was done in a jar filled with common air, and containing a solution of caustic potash in a small capsule, so as to remove any carbonic acid which might be given off by the seeds. In about three days both the wheat and the peas had begun to burst; four out of the six of each continued to grow for about six days, and remained healthy afterwards. The removal of the carbonic acid, then, did not affect the germination. I subsequently found that in this experiment I had almost exactly repeated one of Mr. Ellis's in his 'Inquiry into the changes produced on atmospheric air by the germination of seeds,' &c. He employed peas, and satisfied himself that all the oxygen in the jar had been absorbed by the germinating plants.

SECOND SERIES, VOL. XXII, NO. 64.—JULY, 1856.

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The effect of oxygen on the germination of wheat and peas under the influence of the different solar radiations was also tried. The small colored glasses, having a capacity of 172 to 177 cubic inches, were employed, and the experiments were conducted like those under the colored shades which have been already detailed. The seeds were placed on the bricks on May 2nd. On the 8th, both the wheat and the peas had burst under the colorless glass, but they soon became mouldy, and before the end of the month they were quite dead. The seeds under the yellow glass ran much the same course; but those under the blue glass, though they did not burst till the 11th, grew well, and by the 26th two of the wheat plants had attained a height of 4 or 5 inches. The experiment was discontinued on June 5th. The plants were removed from the brick for desiccation, and on the following day the five of the wheat which had germinated were found to weigh 8 grains, giving an average of 16 grain for each, or an increase of 0.9 grain on the original weight. All the six peas had germinated and weighed 26 grains, giving an average of 43 grs. for each, or an increase of 16 grain on the original weight.

Thus far I have proceeded in the investigation. Many interesting inquiries naturally suggest themselves; some have been already alluded to, for instance, the influence of light upon the colors of flowers; the amount of exclusion of light effected by the soil; the different condition of solar influences required by wheat or by peas at later periods of their growth; and the extension of the observations to other seeds. Other questions might be raised, such as,-What character of light promotes best the absorption of oxygen in germination? At what period in the growth of a plant does oxygen become unnecessary? Is oxygen requisite for the full development of a bulbous-rooted plant? Does carbonic acid act specifically in the prevention of germination, or merely by the exclusion of oxygen? How far does the rapid development of a plant in an early stage interfere with its healthy growth at a later period?

ART. IX.-Reports of Explorations and Surveys to ascertain the most practicable and economical route for a Railroad from the Mississippi River to the Pacific Ocean; made under the direction of the Hon. JEFFERSON DAVIS, Secretary of War.*

UNDER the auspices of the Secretary of War, the reports of the explorations made with reference to a route for the Pacific railroad, are in progress of publication in quarto volumes, excellent in style and full in their illustrations. The results of these surveys are exceedingly varied and important. The physical features and climate of the vast region beyond the Mississippi were examined, animals, plants, and rocks collected, and important contributions thus made to science, while at the same time the special object of the surveys appears to have been pursued with vigor and as much care as the limited time of the surveys admitted. The volume just issued contains the Report of the Secretary of War; an Examination of the Reports of the sev eral routes explored; railway memoranda; and the Report of Governor I. I. Stevens. The further narrative of the exploration, accompanied by views illustrating the features of the country, the natural history and other scientific reports, with illustrations, will appear in other volumes.

The report of the Secretary of War presents a general review of the whole subject, and is drawn up with clearness and apparent justice to each of the proposed routes. The routes examined were five in number:-the most northern or Missouri river route, near the 47th and 49th parallels of north latitude, surveyed under Governor Stevens; the next, or Platte river route, near the 41st and 42nd parallels, examined by Col. Fremont and Capt. Stanisbury, east of the Rocky Mts., and by Lieut. E. G. Beckwith, on the west, from Fort Bridger in 110° W. to Fort Reading on the Sacramento; the third, or Arkansas river route, near the 38th and 39th parallels, explored by Capt. Gunnison's party to the Un-kuk-oo-ap mountains, in longitude 112°, on the Sevier river, where he died; the fourth, or Canadian river route, near the 35th parallel, surveyed under the direction of Lieut. A. W. Whipple; the fifth, near the 31st and 32nd parallels, its different parts under the direction of Capt. Pope, Lieut. Parke, Major Emory, and Lieut. Williamson.

We make the following extracts from the Report of the Secretary of War.

* Reports of Explorations and Surveys to ascertain the most practicable and economical route for a railroad from the Mississippi river to the Pacific Ocean; made under the direction of the Hon. Jefferson Davis, Secretary of War, in 1853-4, according to acts of Congress of March 3, 1853, May 31, 1854, and August 5, 1854. Volume I. 652 pages 4to, with Maps and Tables.