Page:Proceedings of the Royal Society of London Vol 1.djvu/420

Rh ment, as well as the branched and taper roots of those sown in a soil superﬁcially rich, admit of -a. similar explanation. So also when the seeds of the bean were placed to vegetate beneath the mould of an inverted pot, the lower surface of the radicles, being exposed to dry air, were rendered rigid and incapable of emitting ﬁbrous roots; while their upper surface in contact with the mould, being preserved in a due state of moisture, emitted ﬁbres in that direction alone in which proper food was to be procured.

In conﬁrmation of this explanation, the author made a corresponding experiment, in which water was so constantly and abundantly supplied, that every part of the radicles was kept equally wet, and then they emitted ﬁbres perfectly obedient to gravitation, without being inﬂuenced by the soil above them.

The strength of roots, by which they appear to be wisely adapted to their situations of exposure to the violence of winds, is traced by the author to the operation of another cause, noticed in a former memoir; for the immediate consequence of motion upon the roots, as well as upon the branches, is a deposition of alburnous matter upon the part moved; and hence those roots which immediately join the trunk of an insulated tree become strong and rigid, but diminish rapidly in bulk as they recede from the stem and descend into the ground. But in a sheltered valley, on the contrary, where a tree is protected by its neighbours, and little agitated by winds, the roots grow long, and continue slender like the stem and branches, and hence comparatively much less of alburnous matter is expended be- neath the ground.

In the whole of this arrangement the author sees much reason to admire the simplicity of the means employed by the wisdom of nature, but is unable to trace the existence of anything like sensation or intellect in the plants themselves.

Notwithstanding there may be few facts in ancient history which have given rise to more discussion, this subject still appears to the author to admit of elucidation; for though chronologists have availed themselves of the aid which astronomy could give them in ﬁxing the exact time when this event occurred, and thereby ascertaining the dates of several other events, yet among the various periods assigned for this eclipse by different authors, we ﬁnd a difference of no less than 43 years between that assigned by Scaliger, who supposed it to have happened on the 1st of October, 583 B. C. ; and that supposed by Volney, in his Chronologie d’Hérodote. who ﬁxes it on February 3, 626 B. C. The results to which most conﬁdence has been hitherto attached, is, in fact, very nearly the mean between these extremes, and is that preferred by Bayer, in his Chronologia Scythica, published in the Pctersburgh Memoirs for 1728.