. A textbook of botany for colleges and universities ... Botany. GROWTH AND MOVEMENT 457 Advantage. — The benefits of photeolic movements have been van- ously imagined. They have been supposed to prevent injury to the leaves by frost, since the folded position diminishes radiation; or to prevent the formation of dew, so that transpiration may begin promptly in the morning. The difficulty with the first of these ideas is that frost does not occur in the regions where Leguminosae, which exhibit them more strikingly than any other family, most abound; furthermore, a temperature approaching o° C.
. A textbook of botany for colleges and universities ... Botany. GROWTH AND MOVEMENT 457 Advantage. — The benefits of photeolic movements have been van- ously imagined. They have been supposed to prevent injury to the leaves by frost, since the folded position diminishes radiation; or to prevent the formation of dew, so that transpiration may begin promptly in the morning. The difficulty with the first of these ideas is that frost does not occur in the regions where Leguminosae, which exhibit them more strikingly than any other family, most abound; furthermore, a temperature approaching o° C. would render response impossible. The second explanation involves the assumption that transpiration is a valu- 1 i 1 r ) r r r r T^ r r r r f: r r r r T- inaiM \ w \\ y r '/ / r h kj [^ k iLy i r r nWnr L \ \i l1 / I I / mhhi 1 2 4 a 12 18 S 12 18 24 6 12 18 24 6 12 18 24 6 12 18 24 6 12 18 24 6 12 B 24 | Oc later Z2, !£S 2A ZS Z6 27 zs igaT\. Figs. 688,689.—Autographic rec- ords of leaf movements: dates and hours of the day are given below; 12 noon, 24 midnight; the horizontal median line represents the line the recording point would have described had the leaf remained quiet, moving neither toward the diurnal {day) nor the nocturnal {night) positions; the black strips mark the periods of dark- ening, which have no relation to the natural alternation of day and night; 688, photeolic movements of leaf of Alhizzia lophantha; after a period of constant illumination the plant was subjected to 6-hr. periods of alternating darkness and light, then to continuous light, and finally to 3-hr. periods of alternate darkness and light; note the persistence in light (Oct. 25-27) of the movements, which gradually disappear; 689, photeolic and autonomous movements of leaf of Phaseolus vitellimcs^ the latter restricted to the reversed periods of illumination (6 to 6 ) ; note the lag of the response in the former. —After Pfeffer. able function which the plant promotes, inst
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
