Text-book of botany, morphological and physiological . any one of the older members in such a direction that, travers-ing the axis towards the right or the left, it includes the points of insertionof all the successive lateral members according to their age ; the horizontalprojection of this line is called the GaieiicSpiral; in reality it is a helix ^ runninground the stem more or less regularly. Theimportance of this construction has been verymuch overrated, and it has been employedwhere it is not only inapplicable to the eluci-dation of the history of development, but evenwhere it has no lon
Text-book of botany, morphological and physiological . any one of the older members in such a direction that, travers-ing the axis towards the right or the left, it includes the points of insertionof all the successive lateral members according to their age ; the horizontalprojection of this line is called the GaieiicSpiral; in reality it is a helix ^ runninground the stem more or less regularly. Theimportance of this construction has been verymuch overrated, and it has been employedwhere it is not only inapplicable to the eluci-dation of the history of development, but evenwhere it has no longer even a geometricalmeaning, and no longer assists a conception ofthe relative positions, but even makes it moredifficult and complicated. When we are dealing with solitary leaves orshoots standing on the axis in three, four, five,eight, or more directions, and when the diver-gences are not too variable, the construction ofthe genetic spiral is of excellent service for aready understanding of the position of the leaves (Fig. 141); and a more exact. Fig. 141.—Transverse section through the convolu-tion of the leaf-sheaths i—6 of Snbal ambractilifera,in the centre of the section of a young arrangement of the leaves S a ^ the numbers i—6 are united by a line, the geneticspiral is obtained. If the spiral winds from right to left, the right edge of the leaves is called the kathodic, theleft (ascending) edge the anodic ; the reverse in the spiral of an opposite direction seen fromwithout. i-o EXTERNAL CONFORMATION OF PLANTS. knowledge of the peculiarproperties of this ideal line may under these circumstancesbe of great use to morphology. In some cases it may be applied with advantage evento the relative position of whorls. But in a large number of cases other constructionsappear much more natural, since they afford an easier explanation of the relativepositions, and are more in accordance with the phenomena of growth. Theconstruction of the desire
Size: 1463px × 1709px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectbotany, bookyear1875
