Page:An introduction to physiological and systematical botany (1st edition).djvu/126

From Wikisource
Jump to: navigation, search
This page has been proofread, but needs to be validated.
96
COTYLEDONS.

a strong centrifugal force applied to vegetating seeds will considerably divert the root from this direction outwards, while the stem seems to have a centripetal inclination.

The young root, if it grew in a soil which afforded no inequality of resistance, would probably in every case be perfectly straight, like the radical fibres of bulbous roots in water; but as scarcely any soil is so perfectly homogeneous, the root acquires an uneven or zigzag figure. It is elongated chiefly at its extremity[1], and has always, at that part especially, more or less of a conical or tapering figure.

When the young root has made some progress, the two lobes, commonly of a hemispherical figure, which compose the chief bulk of the seed, swell and expand, and are raised out of the ground by the ascending stem. These are called the Cotyledons. Between them is seated the Embryo or germ of the plant, called by Linnaeus Corculum or little heart, in allusion to the heart of the walnut.

  1. As may be seen by marking the fibres of Hyacinth roots in water, or the roots of peas made to vegetate in wet cotton wool.