Nature and development of plants . ther to enable the stemto reach the light. One type of these variations is seen intwining stems, as the morning glory, bean,hop, etc. Young twining plants behave quite like the ordinary plant. The stemsare erect and actively nutating, the apextraveling through a rather large circle inone to three hours. When a certain heighthas been reached the stems are stimulatedby gravity so that their upper portions growmore or less horizontally (Fig. 66). Thisposition is a decided advantage since thestem is now revolved through a larger circle ami has a greater chance of
Nature and development of plants . ther to enable the stemto reach the light. One type of these variations is seen intwining stems, as the morning glory, bean,hop, etc. Young twining plants behave quite like the ordinary plant. The stemsare erect and actively nutating, the apextraveling through a rather large circle inone to three hours. When a certain heighthas been reached the stems are stimulatedby gravity so that their upper portions growmore or less horizontally (Fig. 66). Thisposition is a decided advantage since thestem is now revolved through a larger circle ami has a greater chance of coming intocontact with an object about which it cantwine. As soon as the stem comes into eon-tact with any support its nutation will causeit tO wind or twine about it. Doubtless the contact also act- as a stimulus, causing the stem to bend more energetically. Certainlyin many plants the size and roughness Of per portion of tin the support are important factors in induc-Btem result! jng ,,„. twmmg. \, first the coils are. Fig. (*y Twininghabit of wild tin- horizontalposition of the up- in tin- apex mutatingthrough :t wider circle. I) horizontal hut owing to the elonga- tion of the Stem these coils are gradually pushed upwards and become steep and ver) firmly bound an mud tin support. Twisting of the stems and reflexed bristles often ? in anchoring the plant to its support. It is interesting to Miat in the majorit) of cases tin stem twines about the sup- NATURE OF PLANTS 91 port in left hand spirals or clock wise; less frequently right handspirals are formed, as in the hop, some honeysuckles and knotweeds. Why the growth of the stem results in left or right handtwining is not known but the fact remains that the plants can notbe induced to change their method of twining. 45. The Tendril Type of Stem.—One of the most interestingvariations of climbing plants is seen in those stems that climbby means of tendrils. In this type almost any part of the plantmay bec
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