The naked cells which have been alluded to live in water, and call therefore for no differentiation in connection with this necessity; but those which are surrounded by a cell-wall always develop within themselves a vacuole or cavity which occupies the greater part of their interior, and the hydrostatic pressure of whose contents keeps tha protoplasm in contact with the membrane, setting up a condition of turgidity.
The opening and closing of the stomata is the result of variation in the turgidity 01 their guard cells, which is immediately affected by the condition of turgidity of the cells of the epidermis contiguous to them.
The only way in which their turgidity is modified is by the entry of water into them from the contiguous cells of the general epidermis and its subsequent withdrawai through the same channel.
The great turgidity which is thus caused exerts a considerable hydrostatic pressure on the stele of the root, the vessels of the wood of which are sometimes filled with water, but at other times contain air, and this often under a pressure less than the ordinary atmospheric pressure.
There is set up at once a certain hydrostatic pressure, due to the turgidity which ensues upon such absorption, and the extensible cell wall stretches, at first in all directions.
The increase in surface of the cell wall is thus duefirstly to the stretching caused by turgidity, and secondly to the formation and deposition of new substance upon the old.
The turgidity in the cells of a growing member is not uniform, but shows a fairly rhythmical variation in its different parts.
If the member is one which shows a difference of structure on two sides, such as a leaf, the two sides frequently show a difference of degree of turgidity, and consequently of rate of growth.
This is due to the fact that while young the turgidity and consequent growth are greater in the dorsal side of the leaf, so that it becomes rolled up. As it develops the maximum turgidity and growth change to its upper side, and so it becomes unfolded or expanded.
One side of a stem may be more turgid than the opposite one, and the maximum turgidity, with its consequent growth, may alternate between two opposite sides.
More frequently the region of maximum turgidity passes gradually round the growing zone.
The passage of the maximum turgidity round the stem may vary in rapidity in different places, causing the circle to be replaced by an ellipse.
The response to the stimulus takes the form of increasing the permeability of particular cells of the growing structures, and so modifying the degree of the turgidity that is the precursor of growth in them.
The small pulvini of the leaflets, by similar changes of the distribution of turgidity, take up their respective position.s after receiving the stimulus.
In some cases the two sides of the pulvini vary their turgidity in.
More slowly, but yet in the same way, we may note the change in turgidity of certain cells of the Droscra tentacles, as they close over the imprisoned insect.
To him also belongs the great merit of liberating Russian preaching from the fetters of Polish turgidity and affectation by introducing popular themes and a simple style into Orthodox pulpit eloquence.
While it is not improbable that the collar-pores and the proboscispores may evacuate excretory substances, there can be little doubt that their primary function is to regulate the turgidity of the segment to which they respectively belong.
Organic Rhythm.It is a remarkable fact that during the process of growth we meet with rhythmic variation of such turgidity.
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