Even splits

Usage examples of halves.

As the movements caused by the alternate turgescence of the cells in the two halves of a pulvinus, must be largely determined by the extensibility and subsequent contraction of their walls, we can perhaps understand why a large number of small cells will be more efficient than a small number of large cells occupying the same space.

But the blade itself sometimes curves or moves, of which fact Bauhinia offers a striking instance, as the two halves rise up and come into close contact at night.

Under these circumstances, the whole lower halves of the cotyledons, which had their summits enclosed in the tubes, were fully exposed to the light of the sky, whilst their upper halves received exclusively or chiefly diffused light from the room, and this only through a very narrow slit on one side.

We imagined that at the commencement of the movement it might be determined by one of the two halves of the leaflet being a little heavier than the other.

At night the two halves rise up and close completely together, like the opposite leaflets of many Leguminosae.

Whilst the two halves of the leaf are closing, the midrib at first sinks vertically downwards and afterwards bends backwards, so as to pass close along one side of its own upwardly inclined petiole.

To ascertain whether injury was thus soon caused, the upper halves of 8 cotyledons of Avena were thickly coated with transparent matter,--4 with gum, and 4 with gelatine.

The result was that the lower halves of all became bowed to the light, but generally not in so great a degree as the corresponding part of the free seedlings in the same pots.

Of the remaining 14 cotyledons, the lower halves of which had been fully exposed to the light for the whole time, 7 continued quite straight and upright.

These cleared stripes were not directed towards the window, but obliquely to one side of the room, so that only a very little light could act on the upper halves of the cotyledons.

Cotyledons with their upper halves enclosed in such tubes were placed before a southwest window, in such a position, that the scraped stripes did not directly face the window, but obliquely to one side.

Tubes of the kind just described were placed on several occasions over the upper halves of 27 cotyledons.

It is therefore certain that a little weak light striking the upper halves of the cotyledons of Phalaris, is far more potent in determining the direction of the curvature of the lower halves, than the full illumination of the latter during the whole time of exposure.

Nevertheless, 5 of these 8 cotyledons remained quite upright, although their lower halves were fully illuminated all the time.

These were made by folding goldbeaters' skin once round the upper halves of young hypocotyls, and painting it thickly with Indian ink or with black grease.