. Plant studies; an elementary botany. Botany. 60 PLANT STUDIES to tlio danger. Perhaps the most completely adapted leaves of this kind are those of the "sensitive plants," whose leaves respond to various external influences by changing their positions. The common sensitive plant abounds in dry regions, and may Ije taken as a type of such plants (see Figs. 4, 41, 171). The loaves are divided into very numerous small leaflets, sometimes very small, which stretch in pairs along the leaf branches. When drought approaches, some of the pairs of leaflets fold to- gether, slightly reduc- in
. Plant studies; an elementary botany. Botany. 60 PLANT STUDIES to tlio danger. Perhaps the most completely adapted leaves of this kind are those of the "sensitive plants," whose leaves respond to various external influences by changing their positions. The common sensitive plant abounds in dry regions, and may Ije taken as a type of such plants (see Figs. 4, 41, 171). The loaves are divided into very numerous small leaflets, sometimes very small, which stretch in pairs along the leaf branches. When drought approaches, some of the pairs of leaflets fold to- gether, slightly reduc- ing the surface expo- sure. As the drought continues, more leaflets fold together, then still others, until iinally all the leaflets may be folded together, and the leaves themselves may bend against the stem. It is like a sailing vessel gradually taking in sail as a storm approaclies, until flnally nothing is exposed, and the vessel weathers the storm by presenting only bare poles. Sensitive plants can thus regulate the oxjiosed sur- face very exactly to the need. Such motile leaves not only behave in this mannei' at the coming of drought, but the positions of the leaflets are shifted throughout the day in reference to light, and at night a very characteristic position is assumed (see h'igs. 2, 3, 43), once called a " sleeping ; 'I'lie danger from niglit exposure comes from the radiation of heat which occurs, wliii'li may chill the leaves to the danger })oint. The night position of tlu! leaflets of has l)een re- ferred to already (see §14). Similar cluingcs in the direc- tion of the leaf planes at the coming of night may be observed in most of the Leguminosa;, even the common. Fig. 43. CotylcdoHB of Bqliasli SL-L-dling, show- ing positions in light (left figure) and in darliness (riglit figure).—After Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and
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