Evaporation is thus constantly taking place from the leaves, and if there is no moisture to supply the place of what is lost, the cells collapse and the leaf, as we say, wilts.  When water is again supplied the cells swell and the leaf becomes fresh.

(3) Place two seedlings in water, one with its top, the other with its roots in the jar.  The latter will remain fresh while the first wilts and dies.

Absorption takes place through the roots.  The water absorbed is drawn up through the woody tissues of the stem (4), and the veins of the leaves (5), whence it escapes into the air (6).

(4) Plunge a cut branch immediately into a colored solution, such as aniline red, and after a time make sections in the stem above the liquid to see what tissues have been stained.[1]

[Footnote 1:  The Essentials of Botany, by Charles E. Bessey.  New York, Henry Holt & Co., 1884.  Page 74.  See also Physiological Botany, pp. 259-260.]

(5) “That water finds its way by preference through the fibro-vascular bundles even in the more delicate parts, is shown by placing the cut peduncle of a white tulip, or other large white flower, in a harmless dye, and then again cutting off its end in order to bring a fresh surface in contact with the solution,[1] when after a short time the dye will mount through the flower-stalk and tinge the parts of the perianth according to the course of the bundles."[2]

[Footnote 1:  If the stems of flowers are cut under water they will last a wonderfully long time.  “One of the most interesting characteristics of the woody tissues in relation to the transfer of water is the immediate change which the cut surface of a stem undergoes upon exposure to the air, unfitting it for its full conductive work.  De Vries has shown that when a shoot of a vigorous plant, for instance a Helianthus, is bent down under water, care being taken not to break it even in the slightest degree, a clean, sharp cut will give a surface which will retain the power of absorbing water for a long time; while a similar shoot cut in the open air, even if the end is instantly plunged under water, will wither much sooner than the first.”—­Physiological Botany, p. 263.]

[Footnote 2:  Physiological Botany, p. 260.]

(6) Let the leaves of a growing plant rest against the window-pane.  Moisture will be condensed on the cold surface of the glass, wherever the leaf is in contact with it.  This is especially well seen in Nasturtium (Tropaeolum) leaves, which grow directly against a window, and leave the marks even of their veining on the glass, because the moisture is only given out from the green tissue, and where the ribs are pressed against the glass it is left dry.