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A COMPARATIVE STUDY OF THE PRIMARY VASCULAR SYSTEM OF CONIFERS. II. GENERA WITH OPPOSITE AND WHORLED PHYLLOTAXIS
Author(s) -
Namboodiri Kadambari K.,
Beck Charles B.
Publication year - 1968
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1968.tb07399.x
Subject(s) - phyllotaxis , biology , reticulate , botany , type (biology) , evolutionary biology , shoot , meristem , ecology
This paper reports the results of a detailed comparative investigation of the primary vascular system of seven species of conifers characterized by opposite and whorled phyllotaxis. Three patterns, indicated as types I, II and III, are described. Type I is similar to the sympodial pattern of conifers with helical phyllotaxis. Type III is a reticulate system which results from a fusion of a pair of traces that form the vascular supply to each leaf. Each trace of the pair branches from a separate, adjacent sympodium, and the two traces diverge synchronously in opposite directions. Type II is intermediate between types I and III. It resembles type I in that the vascular supply to a leaf originates as a single trace, and it is similar to type III in that direction of trace divergence may be either sinistrorse or dextrorse. Four species were found to be characterized by both types II and III, the different types occurring in different shoot tips of the same individual. All three types were observed in one species. Where type II occurred in the same plant with either type I or type III, or in the one species in which all types occurred, some leaves were supplied by a trace originating singly, others by a trace originating as a pair of bundles. On the basis of a comparative analysis of the vascular patterns in conifers with helical, opposite and whorled phyllotaxis, including a correlation of the type of vascular pattern with other characters, it was concluded that the reticulate system is probably derived from the open system characteristic of conifers with helical leaf arrangement, that this type of vascular system is composed of sympodia, and that the origin of the vascular supply to a leaf as a single trace is the primitive condition in the Coniferales.