The periodicity of the circumnutating movement often continues for some time in darkness, as we have seen in the last chapter; whilst heliotropic bending ceases very quickly when the light fails.
The heliotropic movements of many other seedlings probably aid them in like manner in emerging from the ground; for apogeotropism by itself would blindly guide them upwards, against any overlying obstacle.
Tropaeolum majus: heliotropic movement and circumnutation of the epicotyl of a young seedling towards a dull lateral light, traced on a horizontal glass from 7.
Whenever irregular ellipses or loops are still formed, their longer axes are almost always directed in the line of gravity, in an analogous manner as occurred with heliotropic movements in reference to the light.
The latter, or heliotropic movements are determined by the direction of the light, whilst periodic movements are affected by changes in its intensity and not by its direction.
Even in the case of ordinary heliotropic movements, it is hardly credible that they result directly from the action of the light, without any special adaptation.
This heliotropic movement manifestly results from the modification of ordinary circumnutation; and every gradation between the two movements could be followed.
There is therefore a great contrast in the degree of illumination of their upper and lower surfaces, and if they were heliotropic they would bend quickly upwards.
Since the workers show no heliotropism it looks as if an internal secretion from the sexual glands were the cause of their heliotropic sensitiveness.
It is to be inferred that as soon as these animals take up food, a substance or substances are formed in their bodies which diminish or annihilate their heliotropic sensitiveness.
If they are kept permanently without food they remain permanently positively heliotropic until they die from starvation.
This heliotropic sensitiveness lasts only as long as they are not fed.
Since plant-cells show heliotropic reactions identical with those of animals, it is not surprising that certain tissue-cells also show reactions which belong to the class of tropisms.
Marine copepods can be made positively heliotropic by the lowering of the temperature alone, or by a sudden increase in the concentration of the sea-water.
In symmetrically built heliotropic animals in which the symmetrical muscles participate equally in locomotion, the symmetrical muscles work with equal energy as long as the photo-chemical processes in both eyes are identical.
The faint light from the sky is sufficient to cause animals which are in a high degree positively heliotropic to move vertically upwards towards the light, as experiments with such pelagic animals, e.
It is therefore erroneous to try to explain these heliotropic reactions of animals on the basis of peculiarities (e.
The writer observed many years ago that winged male and female ants are positively helioptropic and that their heliotropic sensitiveness increases and reaches its maximum towards the period of nuptial flight.
This reflex process agrees in every point with the heliotropic effects of light on plant organs.
Since plants possess no nerves, this identity of animal with plant heliotropism can offer but one inference--these heliotropic effects must depend upon conditions which are common to both animals and plants.
As regards the rate the flashes must succeed one another to produce this heliotropic effect, Mr. Romanes found that sparks passed at the rate of fifty in an hour would cause considerable bending in half an hour.
The Relative Heliotropic Efficiency of Light of Different Wave Lengths.
The Validity of the Bunsen-Roscoe Law for the Heliotropic Reactions of Animals and Plants.
It has further been shown that the prevalent idea that perception and heliotropic excitation are two distinct phenomena is without any foundation.
But in Setaria the excitatory negative impulse is transmitted along the parenchyma which is moderately conducting; the speed of transmission of heliotropic excitation is, according to Pfeffer, one or two mm.
That perception and heliotropic excitation are two distinct phenomena, which depend on different properties of the protoplasm, and which are independent of each other.
The anomaly of an identical organ appearing as positively heliotropic when acted by light from above, and negatively heliotropic when acted from below, is now fully removed.
Thus if "the seedling be illuminated on one side, a sharp heliotropic curving takes place at the apex of hypocotyl.
The experiment described above shows that rise of temperature, by enhancing transverse conductivity, transforms the positive into negative heliotropic curvature.
From the behaviour of these organs we may draw the further conclusion that perception and heliotropic excitation are two distinct phenomena, which depend on different properties of the protoplasm and which are independent of each other.
It has been thought that para-heliotropic action has nothing to do with the directive action of light, since many leaflets either fold upwards or downwards, irrespective of the direction of incident light.
If the cotyledon be shaded and the light be permitted to fall on one side of the hypocotyl, no heliotropic curving takes place.
Strong sunlight brings about para-heliotropic or 'midday sleep' movement, by which the apices of leaves or leaflets turn towards or away from the source of illumination.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "heliotropic" in a variety of sentences. We hope that you will now be able to make sentences using this word.
