The elements of botany for beginners and for schools . er,and is therefore called the Two-ranked occurs in all Grasses, — in Indian Corn, for in-stance ; also, in the Basswood (Fig. 181). Thisis the simplest of all arrangements, and the onewhich most widely distributes successive leaves, butwhich therefore gives the fewest vertical is the 187. Three-ranked arrangement,—;tiiat of allSeJges, and of White Hellebore. Here the secondleaf is placed one third of the way round the stem,the third leaf two thirds of the way round, the fourth _leaf accordingly directly over the
The elements of botany for beginners and for schools . er,and is therefore called the Two-ranked occurs in all Grasses, — in Indian Corn, for in-stance ; also, in the Basswood (Fig. 181). Thisis the simplest of all arrangements, and the onewhich most widely distributes successive leaves, butwhich therefore gives the fewest vertical is the 187. Three-ranked arrangement,—;tiiat of allSeJges, and of White Hellebore. Here the secondleaf is placed one third of the way round the stem,the third leaf two thirds of the way round, the fourth _leaf accordingly directly over the first, the fifth over the second, and so on. That is, three leaves occurill each turn round the stem, and they are separatedfrom each other by one third of the circumference.(Fig. 186,187.) 188. Five-ranked is the next in the series, andthe most common. It is seen in the Apple (Fig. 188), Cherry, Poplar,and the greater number of trees and shrubs. In this case the line tracedfrom leaf to leaf will pass twice round the stem before it reaches a leaf. Fig. 186. Three-ranked arrangement, shown in a piece of the stalk of a Sedge,with the leaves out off above their bases; the leaves are numbered in order, fromItofl. 187. Diagram or oross-seotion of the same, in one plane; the leaves simi-larly numbered; showing two cycles of three. 70 LEAVES. [SECTION 7. This situated directly over any below (Fig. 189). Here the sixth leaf is overthe first; the leaves stand in five perpendicular ranks, with equal angulardistance from each other; and this distance between any two successiveleaves is just two fifths of the circumference of the stem. 189. Tlie five-rauked arrangement is expressed by the fraction |.fraction denotes the divergence ofthe successive leaves, i. e. the an-gle they form with each other: the numerator also expresses the num-ber of turns made round the stemby the spiral line in completingone cycle or set of leaves, namely,V two; and the denominator givesthe number of leaves i
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1887
