. Practical text-book of plant physiology. Plant physiology. 8 NATURE AND RELATIONS OF AN ORGANISM or region which is designed to make the adjustments in response to such stimuli. The irritable system of the plant may be said to be reflective. 13. Sensory Organs and Zones. Ra- diant forces may penetrate the body of the plant easily and reach internal cells almost as readily as external ones. As a consequence of this fact no plants are known which have developed special organs or cells for the reception of stimuli of this character and of gravitation, al- though the last named force is supposed
. Practical text-book of plant physiology. Plant physiology. 8 NATURE AND RELATIONS OF AN ORGANISM or region which is designed to make the adjustments in response to such stimuli. The irritable system of the plant may be said to be reflective. 13. Sensory Organs and Zones. Ra- diant forces may penetrate the body of the plant easily and reach internal cells almost as readily as external ones. As a consequence of this fact no plants are known which have developed special organs or cells for the reception of stimuli of this character and of gravitation, al- though the last named force is supposed to act as a stimulus only upon certain embryonic cells in the tips of roots while certain similar specializations of photo- tropic action are shown. The reception of chemical and mechanical stimuli how- ever, can be accomplished only by peri- pheral protoplasts, and in some species in which instant perception of the stimulus and rapid reaction are of advantage the sensory cells and the motor mechanisms are highly developed with great mor- phological differentiation. This is to be seen in the tentacular formations on the leaves of Drosera, and the epidermal cells of tendrils. Furthermore the cytoplas- mic layer of the cell is probably the functional organ in such action since its position is undisturbed by developmental changes. 14. Transmission of Impulses. The action of a stimulating force upon the sensory elements may give rise to a new molecular motion the effects of which. Fig. I. Diagrammatic rep- resentation of the course of the fibrilte supposed to form the path of transmission in the plerome of roots of, Allium cepa. The thickness of the walls has been exaggerated to bring out the interprotoplastic threads. After 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 MacDougal, Daniel Trembly, 1865
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectplantph, bookyear1901
