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they are well shaded. Professor Hunt believed he had discovered that, by placing a substance between the seed and the light, fitted to stop the transmission of the chemical or actinic rays, the germination of the seeds was arrested. And if so, two things became evident: 1st, that too much of the influence of the luminous

interfered with the growth of seeds; and 2d, that as the deprivation of the soil of the influence of the actinic rays interfered with the vegetative power in the seeds, the presence of them discovered to us the cause of their growth. In other words, that as the luminous rays of the sunbeam are needed in order to the growth of the upward germ of the seed when it has shot up above the soil, so the actinic rays are needed for its growth while it yet lies beneath it. If you deny plants the former, you will destroy their greenness and strength; and if you prevent by any means the latter finding its way freely to where the seeds lie, you will virtually destroy them. This thought has been long held by many scientific men. Thus Dr Fleming, in the peculiarly interesting second volume of the Christian Athenæum (Temperature of the Seasons), writes, -"It may be said, in general, that the mere growth of plants, or the cellular development of the individual, is due to the heat-making rays of the solar beam; so that every other influence exerted in promoting the specific functions of the plant must follow in the train of healthy growth. Thus, the growth of a plant may be carried on to a considerable extent by a proper combination of moisture and heat, even in the dark. But the plant is white; the green matter denominated chromule, or chlorophyll, has not been secreted in the cells, and

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the plant presents an unhealthy appearance. If the same plant be now exposed to the light of day, and especially to the sunbeam, the secretion of the green matter will commence, and the plant recover its characteristic healthy colour. By covering a portion of a leaf with a bit of tinfoil, or any other opaque object, to obstruct the light, then the cells so shaded will cease to generate chromule, and a white spot will make its appearance. While the luminous rays impart to the vegetable tribes their green colour, the same influence retards the germination of seeds (which the actinic rays appear to advance), and hence the covering of soil so necessary for forwarding this important process. In the flowering and fruiting of plants, the heat-making rays of the solar sunbeam exert a preponderating influence." While, however, all agree that light, or the luminous ray of the sunbeam, develops the green in the plant and is not conducive to the germination of seeds, there is not the same agreement in regard to the other allegation, generally credited formerly, and recently put forth with much confidence, that the actinic, or chemical rays of the sunbeam, are indispensable to the quick and healthy germination of the seed. Looking at the Spectra-light, heat, and actinism, it is alleged that the actinic force is greatest in the violet rays already described, that heat is greatest in the red, and light greatest in the yellow rays, and that the actinic force is smallest in the yellow rays, heat in the violet rays, and light in the red. The conclusion from this is, that the influence of the actinic force to develop the germinating power of seeds, will always and in all circumstances be greatest when the medium is violet. Were this true, we can see many other

un

useful applications of the discovery than those which have reference merely to the growth of seeds. The theory has recently been put to the test, and in a paper read before the meeting of the British Association in Glasgow 1855, Professor Daubeny gives the results of the test as favourable to the alleged influence of the chemical rays in promoting the germination of seeds.

“An opinion has gone abroad,” says the Professor, “ and has found a place in several standard treatises, that as the luminous

rays

favour the development of the growing plant, so the chemical rays promote the germination of the seed. One circumstance alone, however, might raise a doubt as to any direct effect having, in the instances reported, been produced by the several solar rays, namely, that, so far as can be collected from the statements given, all the seeds used by Mr Hunt were buried in the ground to the usual depth. Now, I found that a depth of two inches of common garden soil was quite sufficient to intercept the rays of light, so as to prevent the slightest chemical action being exerted upon highly sensitive paper placed beneath it. The improbability, therefore, of a ray of light acting through such a medium, induced me to institute a set of experiments in which the seeds were placed on the surface of moist earth, exposed to the action of particular portions only of the solar spectrum."

In the first instance, sixty-nine seeds were subjected to experiment, namely, fourteen of Clover (Trifolium incarnatum), twelve of Radish (Raphanus rotundus), thirteen of Sun-flower (Helianthus annuus), sixteen of Buck wheat (Polygonum fagopyrum), and fourteen of Barley (Hordeum sativum). The results were, that the seeds shewed forty-six rootlets, and eighteen sprouts of upward growth under violet light; forty-four rootlets and eighteen sprouts of upward growth under green glass; eighty-two rootlets and twenty-four sprouts of upward growth in darkness; thirty-six rootlets and twenty-six upward sprouts under cobalt-blue glass; thirty-two rootlets and seventeen upward sprouts under amber glass; twenty-nine rootlets and seven sprouts of upward growth under ruby glass; and twenty-three of the former and five of the latter under orange glass.

Accordingly,” remarks the Professor on these results, in this series a slight superiority seemed certainly to belong to the violet-coloured medium over the rest, in relation to the number both of the radicles and plumules which appeared; whilst, in respect to the quickness of their germination, the violet and green media were ahead of the rest, although the plumules did not follow in the same order.” When, however, the same experiments were repeated in a north aspect, the same law did not hold good; for out of sixty-nine seeds, fifty-two rootlets and twenty-two upward sprouts appeared under green glass, forty-nine of the former and seventeen of the latter appeared under blue glass, forty-four and seventeen under transparent glass, thirty-nine rootlets and twenty-three upward shoots appeared under violet light. And with respect to the quickness of germination, it appeared that the green stood first in order; that the seeds under blue and violet, and those in absolute darkness, came up next in order, and with nearly equal rapidity; that those in full light were next in order; whilst orange, ruby, and yellow were about equal, but somewhat later than the

rest. It did not appear, therefore, from this last series of experiments, that violet light favoured germination at all more than

any other species of light; nor, indeed, that any kind of ray was injurious to the process, so long as its intensity was not too great, as may be inferred to have been the case in the first set of experiments, where the seeds were exposed to the full rays of the sun in a southern aspect.

A great variety of other interesting experiments on seed through coloured media were made, and the results tabulated. These seem to point to the same conclusion, “that light has very little to do with the germination of seeds."

PHOTOGRAPHY.

IF we carefully examine the history of scientific discovery, it will be apparent that the progress of knowledge is regulated by a constant law. The time appears to be fixed when any new truth shall be born unto man. These laws are far beyond the reach of human intellect; but we are permitted to see that the Eternal One, who regulated the tides of the material ocean, has, in His infinite wisdom, fixed the extent of oscillation, the height and depth of each mental wave, and commanded the great spiritual tide-wave of knowledge to advance in obedience to an undeviating law.

From the earliest periods of history—since man clothed

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