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Telopea Vol. 6(4): 1996 
one level might be a character-state at another, and that states of a character can arise 
from modifications of an existing pathway. For example, in a study of the differences 
m tendril morphology in Pisiim, 'tendril' is the character and 'types of tendrils' the 
states. At a higher level, however, tendril can be seen as a state of the character 
derivatives of a leaf-primordium'. One role of developmental studies then is to 
determine what, if any, are the differences in developmental pathways, and when (at 
what stage) they occur. These modifications can be morphological or heterochronic. 
In order to facilitate temporal and morphological comparisons, the concept of Repeating 
Growth Unit (RGU) was introduced as a morphological unit intermediate between 
metamer and module (Grimes 1992). The RGU is defined as the smallest complete 
repeating or unitary sequence of metamers produced by a meristem. A module is the 
series or sequence of RGUs produced by a single apical meristem. An RGU is the 
same as the module in those cases where an indefinite series of metamers are produced 
which are morphologically and physiologically indistinguishable. The inflorescence 
was defined (Grimes, 1992) as that sequence of metamers of a RGU that participates 
in the production and/or presentation of flowers and fruit. 
Briggs and Johnson (1979) introduced terminology dealing with duration of meristems 
which is followed here. Anthotelic meristems are those that terminate with the 
formation of a flower. Blastotelic inflorescences do not terminate with a flower and 
are divided into two types. Auxotelic axes continue growth beyond the flowering 
region, while anauxotelic ones end in an aborted vegetative apex. 
Defined in the context of Repeating Growth Units (Grimes 1992), shoot dimorphism 
means that different shoots on the same individual are composed of different metamers 
or sequences of metamers. In architectural terminology shoot-dimorphism is a result 
of division of meristem labor (Halle et al. 1978; Tomlinson 1978; Tourn et al. 1992). 
Romberger (1963) defined a bud as an unextended, partly developed shoot having 
at its summit the apical meristem which produced it. Halle et al. (1978, p. 35) 
distinguish a rosette from a bud: a bud is enclosed by bud-scales, a rosette by 
reduced foliage leaves. For descriptive purposes in this paper branch-bud and apical 
bud both are used to refer to the nodes and associated leaf-primordia that are 
congested distal to the first elongated internode, regardless of whether covered by 
bud-scales or foliage leaves. 
A primary bud is the first to develop in a leaf-axil (Cremer 1978); accessory buds 
develop subsequently. Halle et al. (1978) differentiate between primary and secondary 
bud complexes. In primary complexes several meristems are initiated separately 
within a single leaf-axil, most commonly in a transverse or vertical series. Secondary 
complexes are essentially condensed shoot-systems that apparently result from the 
branching of an original solitary lateral meristem. 
Preformed buds (Brown & Sommer 1992; cf. Tomlinson & Gill 1973) are those in 
which the metamers of a morphogenetic unit (which is more or less equivalent to 
RGU) are formed but then undergo some period of dormancy in a condensed state. 
Neoformed buds (Brown & Sommer 1992) are those in which metamers form and 
develop with no period of dormancy. 
The plastochron is the time between the initiation of one leaf-primordium and the 
initiation of the next (Mauseth 1988). For descriptive purposes nodes and 
leaf-primordia are numbered basipetally starting with the one differentiating at the 
apex (first plastochron, first leaf-primordium). 
Heterochrony is the change in relative time of appearance and/or rate of development 
for characters already present in the ancestor (Gould 1977). So, determining that 
there has been a heterochronic change and the polarity of the change requires some 
