Relationships Between Shoot Growth and Changing Phyllotaxy of Ranunculus

Abstract

Growth of Ranunculus shoots through ontogeny is quantified by techniques utilizing scanning electron microscopy and studies on living plant material. The order of the contact parastichy phyllotaxy in the apical system is related to the relative plastochron rates of growth of the shoot. There is a change in the (2, 3) contact parastichy pattern of vegetative phyllotaxy to a transitional (3, 5) contact pattern which is maintained through sepal production. Formation of a 5(1, 1) whorl of petal primordia establishes a (5, 8) contact pattern with the sepal primordia. Subsequent initiation of stamen primordia, in spiral sequence, results in (5, 8, 13) triple contacts between petal and stamen primordia. The stamen primordia and carpel primordia arrangement is characterized by a (8, 13) contact parastichy pattern of phyllotaxy. Through ontogeny the volume of the shoot apex progressively increases but the shape of the apex, described by a second degree polynomial, remains constant. The plastochron and the relative plastochron rates of radial and vertical displacement of primordia progressively decrease during transition but there is no alteration of the chronological rate of apical expansion. The change in contact parastichy phyllotaxy through ontogeny is interpreted as a change in the relative positions of primordia insertion on the apex resulting from an increase in apical volume and an increased rate of primordia initiation.

Capitulum Phyllotaxis and Numerical Canalization in Microseris pygmaea (Asteraceae: Lactuceae)

“…In both Xanthium experiments, divergence angles differed significantly from 137.5°. Variation in the divergence angle is also found in flowers ofRanunculus (Meicenheimer, 1979), and Asteracean flower heads (Fujita, 1939;Ryan, Rouse, and Bursill, 1991). Nelson (1954) has criticized the view that the divergence angle of 137.5°should be constant in flowers.…”

Organ positions and pattern formation in the shoot apex

“…Examples of such factors include the internodal distance between primordia at the shoot apex and the size of a primordium at initiation relative to the size of the meristem. In fact, some studies have shown that changes in these parameters are associated with changes in phyllotaxy (Greyson and Walden, Greyson et aL, 1978;Maksymowych and Erickson, 1977;Meicenheimer, 1979Meicenheimer, , 1981. Although changes in these parameters are associated with changes in organ positioning, whether or not they play a key role in determining phyllotaxy or are simply the result of phyllotaxy has yet to be determined.…”

Phyllotaxie

“…Ce modele syncretise la plupart des modeles phyllotaxiques s'interessant a la disposition helico"idales des feuilles et fleurons avec une divergence constante (Richards, 1951 ;Snow et Snow, 1962 ;Adler, 1974;Thornley, 1975;Williams, 1975 ;Larson, 1977;Mitchinson, 1977;Veen et Lindenmayer, 1977 ;Meicenheimer, 1979). Mais il semble peu compatible avec la theorie des helices foliaires multiples de Plantefol (1948).…”