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The smaller outer scales have no corresponding leaf, and apparently are modified stipules of the leaves of the preceding year, but the larger ones have a leaf to each pair of scales. The outer and inner leaves are small, the middle ones larger. Comparing the branch, it will be seen that these leaves make the largest growth of internode.
The reversal of the curvature occurred at any point in the stem, even in the middle of an internode. Had I not seen this case, I should have thought its occurrence most improbable.
The shoot had now grown 3.5 inches in length, and carried at its extremity a young internode 1 inch in length, which showed slight changes in its curvature. The next or ninth revolution was effected in 2 hrs. 30 m. From this time forward, the revolutions were easily observed.
This was so nearly upright that its revolution could not be easily observed; but it certainly moved, and the side of the internode which was at one time convex became concave, which, as we shall hereafter see, is a sure sign of the revolving movement. I will assume that it made at least one revolution during the first twenty-four hours.
In our present species a young internode, placed in front of a window, made three narrow ellipses, transversely to the direction of the light, at an average rate of 2 hrs. 40 m. When placed so that the movements were to and from the light, the rate was greatly accelerated in one half of the course, and retarded in the other, as with twining plants.
Thus it follows that stems must bear leaves. The marked stems of seedlings show greater growth towards the top of the growing phyton. It is only young stems that elongate throughout. The older parts of a phyton grow little, and when the internode has attained a certain length, variable for different stems and different conditions, it does not elongate at all.
But the movement of each separate internode is so independent of the others, that cutting off an upper one does not affect the revolutions of a lower one.
This species has not the power of spirally twining, which seems due, not so much to a want of flexibility in the stem, as to continual interference from the clasping petioles. An upper internode made three revolutions, following the sun, at an average rate of 1 hr. 46 m.
The thirty-sixth revolution was performed at the usual rate; so was the last or thirty-seventh, but it was not completed; for the internode suddenly became upright, and after moving to the centre, remained motionless. I tied a weight to its upper end, so as to bow it slightly and thus detect any movement; but there was none.
When the movement ceased, the lower internode was 9 inches, and the penultimate 6 inches in length; so that, from the twenty-seventh to thirty-seventh revolutions inclusive, three internodes were at the same time revolving.
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