. The causes and course of organic evolution; . meS CO 3 CO o o • S c3 c . -op- Si. o00 A C5 ^^ c300. — 00 o ca3 2 eJ « _0 r-lTJ CO ^^ O OJ £ cs::: & S o .(J c^ 00 220 Causes and CorRSE of Organic Evolution w-ise in the same position or relation, is more instructive. Herethe gro^-ing stem apex, in elongating further, has respondedapogeotropically by curving upward, but not vertically so,for heliotropism has also been at work, so the resultant direc-tion seen in this figure has been taken. The varying angularpositions, assumed by the leaf stalks as well as the primaryand secondary leaflets, are
. The causes and course of organic evolution; . meS CO 3 CO o o • S c3 c . -op- Si. o00 A C5 ^^ c300. — 00 o ca3 2 eJ « _0 r-lTJ CO ^^ O OJ £ cs::: & S o .(J c^ 00 220 Causes and CorRSE of Organic Evolution w-ise in the same position or relation, is more instructive. Herethe gro^-ing stem apex, in elongating further, has respondedapogeotropically by curving upward, but not vertically so,for heliotropism has also been at work, so the resultant direc-tion seen in this figure has been taken. The varying angularpositions, assumed by the leaf stalks as well as the primaryand secondary leaflets, are most instructive, as exhibitingevery phase of resultant response between diageotropism anddiaheliotropism, in which however the more important latterphase for the leaf surpasses the less important former one. But on bright hot days a third factor may be made evidentin resultant movements of the leaflets, namely parahelio-tropism, or the effort on the part of leaflets to so tilt upwardthat the intense illumination by blue-violet rays may be min-imized. Thus when the sky is clear and the l
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