By geotropism we mean the power possessed by the parts of a plant of growing along lines which make certain angles with the direction of the earth’s attraction.
But geotropism is not a primitive attribute of the plant, and it is even now absent from those plants which, like many Algae, have no definite position.
Geotropism cannot have arisen before plants first became fixed in the earth.
Footnote 97: It will be observed that my way of thinking and experimenting here is related to that which led Knight to the discovery and investigation of the geotropism of plants.
The relations between vegetable and animal geotropism have been more recently investigated by J.
We must think of geotropism as a growth habit of all plants, not caused by light, for it has been shown to act in the dark, but of the greatest advantage to all plants in their initial start toward the light.
Geotropism is one of those mysteries with which the book of nature is crowded, and merely to describe it and realize its force is by no means to arrive at its true inwardness.
If they had been acted on by geotropism or apheliotropism (for the plant was illuminated from above), they would have directed themselves to the centre of the earth.
Sachs has discussed the manner in which geotropism and heliotropism are affected by differences in the angles at which the organs of plants stand with respect to the direction of the incident force.
That this curvature was due to the action of geotropism during the horizontal position of the radicle, was shown after 4 days, when a new tip had been re-formed, for it then grew perpendicularly downwards.
After a time geotropism always prevailed, but its action was often delayed; and in three instances there was a most curious struggle between geotropism and the irritation caused by the cards.
A rather greater length of the radicle is bowed downwards by geotropism than in the case of Vicia faba, [page 536] that is to say, rather more than 6 mm.
In these three last cases geotropism and the irritation caused by the attached squares alternately prevailed in a highly remarkable manner; geotropism being ultimately victorious.
We could, however, observe the movements of stems placed at first only a little from the perpendicular, in which case geotropism did not act with nearly so much power, as when the stems were horizontal and at right angles to the force.
Therefore the cards, affixed to the lower sides of their tips, seemed to produce no effect; and geotropism easily conquered the effects of the irritation thus caused.
The part which is most bowed through geotropism lies at a distance of several millimeters from [page 535] the apex.
Whether this can be of any service to them is very doubtful, but with seeds germinating on the surface it will slightly aid geotropism in directing the radicles to the ground.
This natural current may be allowed to remain, the action current due to geotropism being superposed on it; or the natural current may be neutralised by means of a potentiometer and the reflected spot of light brought to zero of the scale.
Until the existing terminology is revised, it would perhaps be advisable to distinguish the geotropism of the shoot as Zenithotropism and of the root as Nadirotropism.
The very complex type of nyctitropic movement of the primary petiole of Mimosa results from the combined effects of thermo-geotropism and phototropism.
This will be understood from consideration of the number of possible combinations with only two variables, geotropism and phototropism.
A crucial experiment will be described which demonstrates the effect of thermo-geotropism in the diurnal movement of the leaf of Mimosa.
In the case of geotropism the stimulus is constant, but its tropic effect, we shall presently see, undergoes variation with changing temperature.
The effect of geotropism in opposition to phototropism will be found in the following experiments, where the opposing action of light of different intensities is seen to give rise to a partial, to an exact, or to an over-balance.
The effect of geotropism may be strong G, or feeble, g.
But in geotropism the force of gravity is by itself inoperative; it is only through the weight of the cell contents that the stimulus becomes effective.
That geotropism has little effect is seen from the fact that the inversion of flower does not interfere with the normal opening or closing of the flower.
For the removal of various obscurities connected with geotropismit is therefore necessary to elucidate the following: 1.
Heliotropism and geotropism are among the well-known physiological functions of plants: the roots are seen to bend away from the light and towards the ground; the branches behave just in the opposite way.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "geotropism" in a variety of sentences. We hope that you will now be able to make sentences using this word.
