. The elements of botany for beginners and for schools. Plants. 70 LEAVES. [SECTION 7. Tins situated directly over any below (Fig. 189). Here the sixth leaf is over the first; the leaves stand in five perpendicular ranks, with equal angular distance from each other; and this distance between any two successive leaves is just two fifths of the circumference of the stem. 189. The five-ranked arrangement is expressed by the fractioi fraction denotes the divergence of the successive leaves, i. c. the an- gle they form with each other: the numerator also expresses the num- ber of turns made round t
. The elements of botany for beginners and for schools. Plants. 70 LEAVES. [SECTION 7. Tins situated directly over any below (Fig. 189). Here the sixth leaf is over the first; the leaves stand in five perpendicular ranks, with equal angular distance from each other; and this distance between any two successive leaves is just two fifths of the circumference of the stem. 189. The five-ranked arrangement is expressed by the fractioi fraction denotes the divergence of the successive leaves, i. c. the an- gle they form with each other: the numerator also expresses the num- ber of turns made round the stem by the spiral line in completing one cycle or set of leaves, namely, two; and the denominator gives the number of leaves in each cy- cle, or the number of perpendic- ular ranks, namely, five. In the same way the fraction -| stands for the two-ranked mode, and J- for the three-ranked : and so these different sorts are expressed by the series of fractions -|, ^, f. Other cases follow in the same numerical progression, the next being the 190. Eight-ranked arrangement. In this the ninth , leaf stands over the first, and three turns are made [ around the stem to reach it; so it is expressed by V the fraction f. This is seen in the Holly, and in the common Plantain. Then comes the 191. Thirteen-ranked arrangement, in which the fourteenth leaf is over the first, after five turns around the stem. The common Houseleek (Fig. 191) is a good example. 192. The series so far, then, is \, J, f, f, T5g; the numerator and the denominator of each fraction being those of the two next preceding ones added together. At this rate the next higher should be ^, then ^f, and so on : and in fact just such cases are met with, and (commonly) no others. These higher sorts are found in the Pine Family, both in the leaves and the cones and in many other plants with small and crowded leaves. But in those the number of the ranks, or of leaves in each cycle, can only rarely. Please note that these images
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectplants, bookyear1887
