. A compendium of general botany. Plants. 138 COMPENDIUM OF GENERAL BOTANY. conversely, reducing the turgescence of the guard-cells tends to close the pores. Besides this general statement, a few special considera- tions are necessary. It has been observed that the stomata of some water-plants are open at all times whether the guard-cells are tur-. FiG. 79 —Surface-view of a breatliing-pore of Triticum vulgaro. (Open.) (After Schwendener.) Type III. gescent or not. It mnst also be remembered, as has aireaay been stated, that the subsidiary cells in some cases assist in closing the breathing-po
. A compendium of general botany. Plants. 138 COMPENDIUM OF GENERAL BOTANY. conversely, reducing the turgescence of the guard-cells tends to close the pores. Besides this general statement, a few special considera- tions are necessary. It has been observed that the stomata of some water-plants are open at all times whether the guard-cells are tur-. FiG. 79 —Surface-view of a breatliing-pore of Triticum vulgaro. (Open.) (After Schwendener.) Type III. gescent or not. It mnst also be remembered, as has aireaay been stated, that the subsidiary cells in some cases assist in closing the breathing-pores. The opening of pores is also influenced by the pressure of the epidermal cells. Why does the turgor of the guard-cells increase ? First of all sunlight is the outer agency which produces these changes. It is. evident also that the chlorophyll of the guard-cells enters as a fac- tor in turgor. The iwesence of cldorophyll is characteristic of the guard-cells in contradistinction to the other epidermal cells. The delicate structure or other peculiarities of the guard-cells are of hnportance in facilitating diosmosis with neighboring epidermal cells (gymnosperms). The question whether warmth has an effect similar to that which light produces could not be satisfactorily answered by Schwendener^ although he does not doubt that suddenly reducing the temperature ' to zero reduces the turgescence of the guard-cells, while raising the temperature increases it. The mechanism of the coniferous type is still under investiga- tion. {Ij) Lenticels. A knowledge of these structures presupposes a knowledge of cork-tissue. Lenticels are lense-shaped cork-like tissue-formations of the bark which have the peculiarity of always being traversed. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Westermaier, Max; Schneider, Al
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectplants, bookyear1896
