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Show 200 SUMMARY OF CHAPTER. CHAP. III. or other obstacle, as well as any difference in the hardness of the soil, and he will turn from that side; if the earth is damper on one than on the other side he will turn thitherward as a better hunting-ground. Nevertheless, after each interruption, guided by the sense of gravity, he will be able to recover his downward course and to burrow to a greater depth. CHAP. IV. CIRCUMNUTATION. 201 CHAPTER IV. THE 0IROUMNUTATING MOVEMENTS OF THE SEVERAL PARTS OP MATURE PLANTS. Circnmnuta.tion of stems: concluding remarks on-Circumnutation of stolons: aid thus afforded in winding among~;t tho stems of surrounding plants-Circumnutntion of flower-stcms-Circumn uta tion of Dicotyledonous leaves- Singular oscillatory movement of leaves of Dionroa-Leaves of Cannabis sink at night-Leaves of Gymnosperms- Of Monocotyledons-Cryptogams-Concluding remarks on the circumnutation of leaves : generally rise in the evening and sink in the morning. WE have seen in the first chapter that the stems of all seedlings, whether hypocotyls or epicotyls, as well as the cotyledons and the radicles, are continually ciroumnutating- that is, they grow first on one side and then on another, such growth being probably preceded by increased turgescence of the cells. .As it was unlikely that plants should change their manner of growth with advancing age, it seemed probable that the various organs of all plants at all ages, as long as they continued to grow, would be found to circumnutate, though perhaps to an extremely small extent. ~ it was important for us to discover whether this was ~he case, we determined to observe carefully a certam number of plants which were growing vigorously, and which were not known to move in any manner. We commenced with stems. Observations of this kind are tedious, and it appeared to us that it would be sufficient to observe the stems in about a score. of genera, belonging to widely distinct families and mhabitants of various countries. Several plants |