The physiology of stomata

Voorkant
Carnegie Institution of Washington, 1908 - 142 pagina's
 

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Pagina 32 - ... herbaceous leaf illustrates in a striking manner all the physical properties of a multiperforate septum. Regarded from this point of view it is shown that the stomatic openings and their adjuncts constitute even a more perfect piece of mechanism than is required for the supply of carbon dioxide for the physiological needs of the plant, and instead of expressing surprise at the comparatively large amount of the gas which an assimilating leaf can take in from the air, we must in future rather wonder...
Pagina 32 - ... diaphragm, whose apertures are so far reduced in size as to materially interfere with the mass movement of the diffusing substance. A section of the paper is devoted to the application of these new observations to the processes of gaseous and liquid diffusion in living plants, and it is pointed out that the structure of a typical herbaceous leaf illustrates in a striking manner all the physical properties of a multiperforate septum. Regarded from this point of view it is shown that the stomatic...
Pagina 86 - He concluded, however, that xerophytic leaf structure (of the hardy evergreens) is not always incompatible with abundant transpiration, but sometimes exists only for use in emergencies, to protect the plant from injurious loss of water.
Pagina 32 - ... possess all the remarkable properties which had been anticipated. The material used for the septa was very thin celluloid, which was perforated at regular intervals with holes of about 038 mm. in diameter. Details of a number of experiments with such diaphragms are given, in which it is shown that they may be so arranged as to produce but little obstructive influence on the diffusive flow of a gas when the total area of the apertures amounts only to about 10 per cent, of the area of the septum,...
Pagina 58 - ... under the microscope but the rapid closing of the stoma in the case of plants standing in the shade suggests that possibly the balance between the tensions is so delicate that the least disturbance of the equilibrium, as in making the sections for examinations, may bring about the closing. It is also possible that, owing to the activity of the secreting cells and the accumulation of intracellular water, the stomata may open at varying periods and after the escape of the vapor close again.
Pagina 65 - ... conclusion that no serious error was being introduced through the fluctuations of the hmidity. A few measurements are given in Table IV., of the transpiration of plants in the dark. Occasionally there is apparent a rhythm corresponding to the daily periodicity, but on the other hand it not unfrequently happens that there may be an irregular decline from the start or the curve may be characterized by a rise or fall without reference to the period of the day. I have noticed on several occasions...
Pagina 125 - My conclusion is, therefore, that the presence or absence of CO2 has no direct influence on stomata, and that, physiologically, they are not at all dependent upon photosynthetic processes within the guard-cells. If this is true, the guard-cell is set off as distinct physiologically from the chlorenchymacell. . . . The mere fact that stomata open in the absence of CO2 shows conclusively that the movement is not directly connected with photosynthetic activity, even if the process takes place normally...
Pagina 125 - ... is, therefore, that the presence or absence of CO2 has no direct influence on stomata, and that, physiologically, they are not at all dependent upon photosynthetic processes within the guard-cells. If this is true, the guard-cell is set off as distinct physiologically from the chlorenchymacell. . . . The mere fact that stomata open in the absence of CO2 shows conclusively that the movement is not directly connected with photosynthetic activity, even if the process takes place normally in the...
Pagina 65 - ... dark. Occasionally there is apparent a rhythm corresponding to the daily periodicity, but on the other hand it not unfrequently happens that there may be an irregular decline from the start or the curve may be characterized by a rise or fall without reference to the period of the day. I have noticed on several occasions that pronounced maxima may be found early in the morning — between 5 and 9 o'clock. Manifestly little importance is to be attached to the results obtained under such conditions...
Pagina 137 - By this means it has been found that the rate of transpiration may undergo sudden and wide changes without the accompaniment of a sufficient change in the dimensions of the stomata to account for them on the theory of stomatal regulation of transpiration.

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