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[In the hand of Francis Darwin:] 58P Power of movement in Plants

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Megarrhiza

Megarrhiza Californica. The manner of germination of this gourd is so extraordinary that the case deserve description. Our attention was called to the case by Prof. Asa Gray, who has been [misinformed] on some important particular & also was so kind as to send us seeds. What takes place will best be understood by giving our special case: a one of the large seeds was laid on the surface of soil under a bell-glass with good bottom peat & on early in morning Jan 10th the radicle protruded & bent down at right angles so as to penetrate the ground. This after consists continued gr which so called radicle consists, as well of hypocotyl & radicle together which cannot be distinguished, & it continued going down & penetrating the earth until about 1/2 inch in length; but the exact length to which the 2 are at this period developed was not ascertained, as we had not specimen enough to make section of. During the Now a remarkable change is the laws manner of growth began, the radicle & hypocotyl [second] or almost [second] to growth grow, while the 2 petiole of the cotyledons (which like all hypogean cotyledons remain for ever in [illeg] the seed-coats) which are completely confluent & form a hollow tent, grow at such a rate at its lower end, that by noon on the 14th, it was 2.35 inches in length, whereas the

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Megarrhiza

radicle & hypocotyl together were only .8 inch in length, & had therefore increased very little. It was manifest by the appearance of the lower part of the tubular petiole, that it was this part which grew. Now the radicle took up the growth & 2 days afterward ie 16th it was not far short for twice a long as on the 14th & secondary radicle was beginning to protrude. In the 17th the radicle was trice as long as on the 14th & On this day the tubular petioles showed a vestige of  a split just above the hypocotyl. On the 18th the seedling was carefully examined, & the tubular petiole were exact 2.5 inch in length, so that they had increased since the 14th only .15 inch' whereas the radicle & hypocotyl, (along the whole length of both about secondary radicle had protruded) together with 2.65 inch in length instead of only .8 of inch as on the 14th. We then see clearly that the radicle first grew, is then arrested in its growth, whilst the tubular petioles grew, & then reassume by rapid growth when these have attained their full length, the radicle grow very rapidly. It has been said that on 17th the base of the tubular petiole was beginning to split, & on the 18th summit of filament was beginning to protrude— The plumule had grown .3 of inch

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up the tube & then the top had bowed itself down almost into a right angle & the force thus exerted caused the convex elbow to protrude thought the split, & thus in an arched form it v would reach the surface of the ground in the usual manner. Here we have another use of the arching of the tip.

We see that the tubular petiole acts like a root in penetrating the ground & carries the summit of the real radicle to the depth beneath the ground. It is well known The petioles resemble roots in being thickly clothed with hairs like root-hairs. It is known that when ordinary seedlings are placed in a sol. of permanganate of potash, the radicle is coloured dark brown whilst the hypocotyl remain inclosed: a seedling with of almost the plumule had just reached the surface was placed in the solution & it was very curious to see that the whole of the whole of the tubular petioles, with their hair, the hypocotyl & radicle all were coloured brown, whilst the apicotyl remained inclosed. So that in the petioles

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in the state of time surface resemble radicles.

Lastly my seed was soon at various depths & some left on the actual surface & in no case were the cotyledon lifted up above the soil, though in one instance the seed was tilled up, owing to some difficulty in the petioles penetrating the ground, but this may occur with any seed whatever. Asa Gray supposed that the seeds were lifted up in the air, but in none of my young specimen was the tubular petiole rigid enough for this work.—

What can be the use of the coherence of the petiole into a tube which acts like a root & petiole to ground of which no parallel case is known?

The root is then lengthened 2 1/2 inches, but this could easily have been effected by its own growth. The plumule is protected from all enemies till it reaches the surface, but then it appears as tender & is equally exposed to danger as a plumule emerging from any ordinary depth. The case probably lies in the root as early age enlarging much & ultimately attaining "huge dimensions"; for it will at

is this correct??

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least at first be protected from the weather & all enemies, whether quadruped, birds, insects or slugs by a covering 2 1/2 inches in thickness of earth, for it has been carried pushed down to the depth by the growth of the petioles. This seem the most probable explanation of the extraordinary manner of generation of these seeds; but whether the gigantic roots when old become exposed & whether they use them at all protected by toughness or a bitter tase, common with family we know not.—

(Jan 24th to May The tip of plumule have now lifted sand & it is beautifully bowed so that tip parallel to lower part.— it soon afterwards straighten itself)

(The intermittent growth of the corr parts of the corresponded root seen t is a curious phenomenon, for it is evidently adapted to allow of the tubular petiole penetrating the ground: if the true radicle had gone on growing in its usual fashion, viz little of the extra tip, the move now rapidly behind again increasing, it wd have penetrated the ground but wd have not been permitted the petiole to do so, nor wd it have dragged the petiole downwards.