[50i]

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[2]

[Draft of Power of Movement in the hand of Francis Darwin with corrections by Darwin]

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as suspect that the immediate progenitor of this species did not possess lateral leaflets, & that their appearance in an almost rudimentary condition at a somewhat more advanced age is the result of reversion to a trifoliate predecessor. However this may be, the rapid circumnutating or gyrating movements of the little lateral leaflets, seems to be due proximately to the pulvinus, or organ of movement, not having been reduced nearly so much as the blade, during [illeg] the changes successive modifications which the species has undergone.

(We now come to the highly important class of heliotropic movements due to the action of a lateral light. When stems, leaves, & other organs are thus placed to a lateral light, so that one side is illuminated more brightly than the other, they bend towards the light. Such heliotropic This movements is manifestly the results from the modification of ordinary of modified circumnutation; and every gradation between the two movements can be followed. When the light was dim & only a very little brighter on one side than on the other, the heliotropic movement consists of a succession of ellipses,

[3]

(38

Ch XII

that the lower part of the cotyledon of Phalaris &c., which in the part that normally becomes most bent towards the light, may be brightly illuminated during many hours & will not bend in the least, if all light be excluded from the tip. It is an interesting experiment to place caps over the tips of the cotyledons of Phalaris, & to allow a very little light to enter through a minute orifices orifices on one side, of the tip of the a cotyledon of Phalaris, & the lower part will then bend to this side, & not to the side whence the light proceed by which the lower part has been brightly illuminated during the whole time.) In the case of the radicles of Sinopsis alba, sensitiveness to light also resides in the tip, which when thus excited, causing the upper part to bend away away from its source.)

(Gravitation in like moreover excited the most light excites the different parts or organs of plants to move curve bend away from the centre centre of the earth, or towards it, or to place themselves in a transverse position. Although it is impossible to modify in any direct any direct manner the attraction of gravity gravity, yet its influence could be

[4]

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