. Botany of the living plant. Botany. 13^2 BOTANY OF THE LIVING PLANT or Venus' Fly-Trap [Dionaea) (Fig 92). These plants show elaborate though different mechanisms for the capture of insects, which are subse- quently digested, and the materials absorbed as nourishment. In the former the action is slow, in the latter its success depends upon rapidity. Drosera bears on its spathulate leaves numerous radiating tentacles, each terminating in a spherical gland, which secretes a viscid juice. (Fig. 91.) This acts like birdlime, detaining any small insect that touches it. The contact-stimulus, confi
. Botany of the living plant. Botany. 13^2 BOTANY OF THE LIVING PLANT or Venus' Fly-Trap [Dionaea) (Fig 92). These plants show elaborate though different mechanisms for the capture of insects, which are subse- quently digested, and the materials absorbed as nourishment. In the former the action is slow, in the latter its success depends upon rapidity. Drosera bears on its spathulate leaves numerous radiating tentacles, each terminating in a spherical gland, which secretes a viscid juice. (Fig. 91.) This acts like birdlime, detaining any small insect that touches it. The contact-stimulus, confirmed by chemical stimulus from substances dissolved, is conveyed to other tentacles than those first touched, and movements of curvature result, so that the tentacles close in and envelop the victim. It is thus covered over by the glandular secretion, and digestion follows. Here the response is in a mature organ, and it is relatively slow; the stimulus is conveyed from the point of con- tact to a distance, where the reaction takes place, as atem- porary curvature of the ten- tacles. But the exciting cause is contact^ confirmed by the pre- sence of a digestible substance. In the case of Dionaea, rapidity of movement is the chief factor in success. Each of the rosette of leaves of the plant bears at its distal end a two-flapped mechanism, like the covers of a book, mubile along the median line as a hinge (Fig. 92). The flaps are furnished with marginal spines, while three sensitive bristles rise erect from the upper surface of each. A touch on any of these six bristles sets the mechanism in motion. If conditions of temperature be favourable the flaps suddenly close together. An insect touching them would be captured within the trap; and as the inner leaf-surfaces are furnished with secreting glands, the digestion follows, with absorption of the soluble substances of the insect-body. Here the stimulus applied at the tip of the bristle is amplified by mechanical leverage, which com
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
