. A compendium of general botany. Plants. •284 COMPENDIUM OF GENERAL BOTANY. iion in mechanics and mathematics. The study of this problem was begun by von Mohl and Palm, and continued by Charles Darwin and H. de Vries. Great advances in this study have recently been made by the investigations of Schwendener, Baranetzky, and Ambronn. The following explanation is based upon the results of Ambronn's and Schwendener's investigations. The active factors in twining are (1) circumnutation of the growing stem-apex and the resistance of the support; (2) nega- tive geotropism. Both factors aid each othe
. A compendium of general botany. Plants. •284 COMPENDIUM OF GENERAL BOTANY. iion in mechanics and mathematics. The study of this problem was begun by von Mohl and Palm, and continued by Charles Darwin and H. de Vries. Great advances in this study have recently been made by the investigations of Schwendener, Baranetzky, and Ambronn. The following explanation is based upon the results of Ambronn's and Schwendener's investigations. The active factors in twining are (1) circumnutation of the growing stem-apex and the resistance of the support; (2) nega- tive geotropism. Both factors aid each other in their effects. Circumnutation makes seizure of or contact with the support possible ; subsequently it is necessary that the contact-stimulus should continue upward and that the curvature should be con- tinuous for a time at least. The advancing of the contact-point is induced by the return pressure of the suj)- port. The support exerts a radial pressure outward against the point of contact behind a (Fig. 171), which necessarily increases and extends the contact area at /i. Antidromic torsions prevent a stem-portion as at ;/, which must become somewhat elongated on the side facing the support due to the pressure of the support, from elongating equally on the outer side when it comes into the j)osition /?. Negative geotropism causes the horizontally or diagonally placed apical stem-portion to curve upward and again brings it in contact writli the support at some point higher up, when the effects of "the pressure will again come into play, as has just been ex- plained. Negative geotropism also assists in another way in forming permanent spirals. It causes curvatures by the more active growth of a continuous tissue-portion which describes a homodromic sj^iral line around the stem. We have yet to mention the influence of apjDarent' and real torsion in the process of twining. According to Ambronn and Schwendener, apparent torsion causes spiral curvatures, which. ' Au appa
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectplants, bookyear1896
