. A manual of structural botany; an introductory textbook for students of science and pharmacy. Plant morphology. THE ALTERNATE OR SPIRAL ARRANGEMENT 197 Orthostachy. Thus, if leaf No. 4 is the next in the orthostachy, to which leaf No. 1 belongs (Fig. 574), three leaves will belong to that cycle. A cycle containing three leaves makes but one turn of the stem. A cycle is expressed in the form of a fraction, its numerator indicating the number of times it encircles the stem, its denominator the number of leaves which it includes, so that the cycle last described must be indicated by the fractio
. A manual of structural botany; an introductory textbook for students of science and pharmacy. Plant morphology. THE ALTERNATE OR SPIRAL ARRANGEMENT 197 Orthostachy. Thus, if leaf No. 4 is the next in the orthostachy, to which leaf No. 1 belongs (Fig. 574), three leaves will belong to that cycle. A cycle containing three leaves makes but one turn of the stem. A cycle is expressed in the form of a fraction, its numerator indicating the number of times it encircles the stem, its denominator the number of leaves which it includes, so that the cycle last described must be indicated by the fraction one-thu'd. The angular divergence of its leaves is 120 degrees. If the next leaf in the same orthostachy as No. 1 be No. 6 (Fig. 572), then that cycle will contain five leaves. A cycle containing five leaves makes two circuits of the stem, so that its exponent. Fig. 570. Decussating opposite leaves. 571. Alternate or spiral leaf-arrangement. 572. Diagram of the same, the i^ arrangement. 573. Diagram of 570, showing its 4 orthostachies. 574. The ^ spiral. 575. The ^ spiral. will be two-fifths. If the second leaf of the orthostachy were No. 9, the appropriate fraction would be three-eighths, the cycle making three turns and containing eight leaves (Fig. 575). It will thus be observed that these fractions form a series, in which each possesses a numerator equal to the sum of the numerators of the two preceding and a denom- inator equal to the sum of the denominators of the two preceding. No cycles occur among the higher plants with which we are concerned, which can be indicated by any fraction not thus formed. Noticing these fractions still further, we observe that the denomi- nators will indicate the number of orthostachies upon the stems which. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Rusby, Henry Hu
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