On whorled phyllotaxis. II. Late binding whorls of Peperomia
Recueil des travaux botaniques néerlandais , Volume 22 - Issue 1/2 p. 128- 172
a. In all Peperomia spp. observed, the phyllotaxis is of the normal Fibonacci series; in several cases the divergence seems to be about 140°. b. In many P. spp. this phyllotaxis remains visible, unaltered and undisturbed. c. In other P. spp. binding whorls are formed out of the spirally arranged vegetative leaves: in forming these whorls every leaf is united to its two lateral neighbours. d. The binding of the leaves probably sets in late during the development and is rather lax. This opinion was based on the small amount of metatopy both in horizontal and in vertical sense of the leaves. If torsion of the axis really never occurs — and untill now it has not been reported — this may be a consequence of the lax coherence of the leaves. e. As only those leaves will be “neighbours” to a certain leaf, which lie with it on the same parastichies of such a kind, as may be the contact parastichies at the moment of whorl formation, the attachments will follow in many cases only in the direction of two sets of antidromous parastichies. The consequence of it will be that 2- 3- and 5-merous whorls are formed. In other cases the binding will be possible in the direction of three sets of parastichies, but one set of parastichies will be most fit for the origin of bindings. In those cases whorls with other numbers of leaves, as 4 or 6, will be possible. Whether a species will product chiefly one kind of whorls or another will depend on the relative sizes of leaves and apex at the moment of whorl formation. f. In the so formed whorls the binding causes a certain amount of metatopy in a longitudinal sense. In di- and trimerous whorls, and as far as I saw often in tetramerous whorls too, the leaves become to the eye perfectly placed at the same level; in pentamerous and hexamerous whorls there remain .characteristic differences in height of insertion. The binding may cause too a metatopy in a horizontal sense; in the dimerous and trimerous whorls we did not perceive it, but in the tetramerous it was clearly to be perceived and in the pentamerous and hexamerous whorls it was so strong as to make the leaves in the whorl horizontally equidistant. g. In our material no tendencies to cause an alternation or a superposition of the whorls were to be observed, the position of the whorls with respect to each other was so as might be derived from an original divergence of about 135° or 140°. h. In the whorls the original spiral may be recognised by the following means. In dimerous whorls we observe an approachment of the leaves of every pair at one side of the stem; this phenomenon is transmitted in a secondary parastichy antidromously to the basal spiral. In trimerous whorls we have analogous approachments ascending after a ternary parastichy, in the same direction as the basal spiral. In tetramerous whorls one of the four distances is sometimes markedly larger than the other three; this phenomenon is transmitted in the way of a distichous phyllotaxis, so that the large space in the third whorl is right over that of the first whorl. Together with other characteristics this may betray the original spiral. In pentamerous whorls we may have differences in the height of insertion, two of the leaves of every whorl being placed somewhat higher: the transmission of these irregularities is antidromous to the basal spiral. In hexamerous whorls there are three higher and three lower leaves, alternating regularly in every whorl; the lower leaves of the next whorl are placed over the lower leaves of the whorl beneath, so that three orthostichies of lower leaves and three of higher leaves are to be observed. In connection with other means this may help us in establishing the original spiral. In branching shoots only the first two leaves of a whorl in most cases give rise to a branch; these branches mostly show diminishing sizes according to the sequence of their subtending leaves in the basal spiral. In shoots, arising from the soil the leaves of the first whorl of vegetative leaves show considerable differences in size according to their sequence in the spiral, the lowest numbers being the smallest, the following ones assuming gradually the normal shape and size of vegetative leaves. In growing non-flowering shoots the expanding leaves diminish in size according to their sequence in the spiral. In flowering shoots the last vegetative leaves under the inflorescence even when full grown show diminishing sizes according to the same sequence. i. The only prophyll or the two prophylls of every lateral shoot are placed laterally; the basal spiral starts from the first of them and runs opisthodromously to the second prophyll or to the first leaf. The first leaf of every shoot is therefore placed either nearly opposite the only prophyll, somewhat backward, or when there are two prophylls, at the frontside of the shoot, nearer to the first prophyll. In those cases where there is only one prophyll the direction of the basal spiral is, in consequence of what has been said, left-handed after a prophyll at the right and inversily. j. The bracts in the inflorescence are formed according to the same phyllotaxis as the vegetative leaves, and as the whorl-forming factors do not prevail there, the normal phyllotaxis comes again to light, the direction of the basal spiral being the same as in the vegetative leaves. k. The lateral branches of Peperomia, though being formed in the axils of whorled leaves, have a certain tendency to be antidromous to their main axis, this furnishing a new argument for the real existence of a spiral in the whorled part.
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J.C. Schoute. (1925). On whorled phyllotaxis. II. Late binding whorls of Peperomia. Recueil des travaux botaniques néerlandais, 22(1/2), 128–172.
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