Text-book of botany : morphological and physiological / by Julius Sachs ; translated and annotated by Alfred W. Bennett ; assisted by W.T. Thiselton Dyer.

Date:
1875
Catalogue details

Licence: Public Domain Mark

Credit: Text-book of botany : morphological and physiological / by Julius Sachs ; translated and annotated by Alfred W. Bennett ; assisted by W.T. Thiselton Dyer. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    that in this case also water escapes from the cells into the intercellular spaces, especially because he was able to determine that a flaccidity of the tissue results from the irrita- tion. In proportion as water escapes from the parenchymatous cells does the whole tissue contract from the elasticity of the cell-walls, of the stretched central bundle, and of the epidermis. That the contraction is in this case so considerable depends on the greater extensibility of the cell-walls and of the delicate central fibro-vascular bundle in Mimosa, which is stated by Pfeffer to be on the contrary but slightly extensible1. 2. Mechanism of the changes caused by ’variation in the temperature and in the intensity of the light. (a) The Opening and Closing of Flowers. With the exception of a few statements by Dutrochet, and the observation by Hofmeister2 that the flowers of the tulip open with an elevation and close with a depression of temperature, scarcely anything is at present known regarding the mechanism of these movements. I can now only make a few general remarks which Pfeffer has placed at my disposal; they are based on a series of investigations which is not yet completed. The opening of the flowers is connected, in the crocus, tulip, and dandelion, with an increase in length of the inner side of the perianth-leaves; there is no considerable increase of the length of the outer side; the part where the curvature takes place is always below. Under the ordinary conditions of vegetation these movements are not caused by a change in the amount of moisture in the air, since they take place even under water. In Crocus •vernus and Tu/ipa Gesneriana and sylasestris small variations of temperature give rise to remarkable movements, every rise causing the flowers to open, every fall to close. The crocus is especially sensitive even to variations of half a degree C. The opening takes place whether the rise is rapid or slow, and both phenomena may be repeated many times in a short space. As in analogous phenomena, there are here also superior and inferior limits, and a temperature of greatest sensitiveness. The crocus, for instance, only opens above 8° C.; at a temperature above 28° C. any rise causes the flowers to close. When the temperature is constant a sudden change in the amount of light causes movements in the crocus, tulip, and Compositae, an increase making them open, a de- crease making them close; but slight changes of temperature may reverse the move- ments in the case of the crocus and tulip. Spontaneous periodic movements also occur in the two latter plants, although not considerable in amount; more so in other species that will be named. Ornithogalum umbellatum, Anemone nemorosa and ranunculoides, Ranunculus Ficaria, and Malope trifida also manifest similar phenomena resulting from changes of temper- ature at any time of the day, but not so strikingly as in the case of the crocus. The phenomena are somewhat different in the dandelion and other Compositae and in Oxalis rosea; in the evening a considerable rise of temperature (e.g. from 90 to 30° C.) does not cause the flowers to open, although a slight but scarcely perceptible curvature outwards results. In the morning, on the contrary, an increase of temperature acceler- ates the opening to a very remarkable degree. If flowers of the dandelion are kept in the dark in the day-time at a temperature below io°C., they scarcely open at all; but in the evening open rapidly and entirely if the temperature is raised; the next morning they are again closed at the ordinary temperature; and when this is raised they do not open at all or only very slightly. The flowers of some other Compositae and of Oxalis, 1 [The most recent experiments of Pfeffer on the stamens of Cynara Scolymus and Centaurea Jacea show that the filaments are irritable along their whole length. Irritation caused a contraction of from 8 to 22 p. c. in length, accompanied with but a very slight increase in thickness, the diminution in mass being caused by an escape of water into the intercellular spaces, which oozes out when the filament is cut through. If the intercellular spaces are filled with water by injection the stamens are no longer irritable.—Ed.] 2 Hofmeister, Flora, 1862, p. 517; Boyer, Ann. des Sci. nat. 1868, vol. IX.