. Text-book of botany, morphological and physiological. Botany. 196 MORPHOLOGY OF MEMBERS. be accurately estimated by an apical view from above, it must remain uncertain whether the position of the mature members is unchanged, or has been altered by lateral displacement and torsion of the axis. A displacement, for instance, of about 90 would be sufficient to alter the divergence from f to f, a similar displacement of 1 -3° would change the divergence from T5^ to ^RT. When the phyl- lotaxis is very -complicated and the number of the longitudinal rows very large, extremely smaH and almost inappr
. Text-book of botany, morphological and physiological. Botany. 196 MORPHOLOGY OF MEMBERS. be accurately estimated by an apical view from above, it must remain uncertain whether the position of the mature members is unchanged, or has been altered by lateral displacement and torsion of the axis. A displacement, for instance, of about 90 would be sufficient to alter the divergence from f to f, a similar displacement of 1 -3° would change the divergence from T5^ to ^RT. When the phyl- lotaxis is very -complicated and the number of the longitudinal rows very large, extremely smaH and almost inappreciable distortions are sufficient to destroy the original arrangement, and to bring into existence altogether different systems of parastichies. This observation is of in- terest so far as it makes it seem doubtful whether certain complicated phyllotaxes are always due to the original arrange- ment of the members1. (4) It must be observed whether the position of newly-formed members or the subsequent change shows any relation to the direction of the force of gravitation, of the light which falls upon them, or of any pressure acting from without2. The effect of the force of gravitation is that primary shoots which are in the main upright put forth leaves spreading on all sides; while such as have a decidedly horizontal growth, in which a rooting under side is contrasted with an upper side, usually show an ar- rangement of leaves on the latter in two rows, or one which is divided into two equal halves by a plane cutting the stem longitudinally, as Saivinia, Mariika, Poly- podium aureum, Pteris aquilina, &c. When vertical primary, shoots with leaves in several rows bear secondary horizontal branches with leaves in two rows, this relationship is less clear, as in the cherry- laurel, ^sweet chestnut, hazel, &c, because an influence independent of gravitation must in these cases be presumed to be exercised by the primary upon the lateral axis, as is shown by the position of
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1882
