Introduction to structural and systematic botany, and vegetable physiology, : being a 5th and revedof the Botanical text-book, illustrated with over thirteen hundred woodcuts . the aperture. The mechanism of the opening and shutting of sto-mata has been recently investigated by Mohl (in Bot. Zeitung for 1856, p. 697,— an abstract of the memoir is given by C. F. Stone in Amer. Journal of Sci-ence for March, 1857), — and these facts verified. The peculiar change of theguardian-cells in form seems not entirely susceptible of mechanical explanation,and is partly controlled (like other vegetable mo
Introduction to structural and systematic botany, and vegetable physiology, : being a 5th and revedof the Botanical text-book, illustrated with over thirteen hundred woodcuts . the aperture. The mechanism of the opening and shutting of sto-mata has been recently investigated by Mohl (in Bot. Zeitung for 1856, p. 697,— an abstract of the memoir is given by C. F. Stone in Amer. Journal of Sci-ence for March, 1857), — and these facts verified. The peculiar change of theguardian-cells in form seems not entirely susceptible of mechanical explanation,and is partly controlled (like other vegetable movements) by the light of thesun; but it mainly depends upon endosmose. Mohl has clearly shown that,while the guardian-cells themselves act so as to open the stomate in moistureand close it in dryness, the adjacent cells of the epidermis in swelling whenmoist tend to close the stomate, and their contraction when dry to open it; —so that the actual position at any time is a resultant of nicely adjusted opposingforces. FIG. 225. A highly magnified piece of the epidermis of the Garden Balsam, -with threestomata (after Brongniart). THEIR STOMATA OR BREATHING-PORES. 151. is in a moist atmosphere, and is freely supplied with sap, the sto-mates remain open, and allow the free escape of moisture by evap-oration. But when the supply fails, and the parenchyma begins tobe exhausted, the guardian-cells, at least equally affected by the dry-ness, promptly collapse, and by closing these thousands of aperturescheck the drain the moment it becomes injurious to the plant. 269. As a general rule, the stomata wholly or principally belongto the epidermis of the lower surface of the leaf: the mechan-ism is too delicate to work wellin direct sunshine. The posi-tion of the stomata, and theloose texture of the lower pa-renchyma, require that this sur-face should be shielded from the suns too direct and intense action;and show why leaves soon perish when artificially reversed, and pre-vented from
Size: 2325px × 1075px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorgra, bookcentury1800, bookdecade1860, booksubjectbotany
