Plant form: an illustrated guide to flowering plant morphology

An

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Illustrate)

Flowering Plant Morphology

ADRIAN

D. BELL

With line drawings by

ALAN BRYAN

s>80

I

Plant branch construction: introduction A case is made (216) for the constructional organization of a flowering plant to be considered in

terms of the potential, position, and time of

activity of shoot apical meristems, or buds.

The

branches and twigs borne on

usually imply something relatively big but not as

environmental fluctuations.

all

conforming

'rules',

and

because

reflecting

its

unique

history. In order to recognize

useful to identify

its

and it is

component branching units and then the manner

(units of construction 282), in

which these are added to or lost from the is more readily appreciated.

developing structure This section

is

heavily biased towards a

'architecture' as

it

has come to be referred

it is

to

the range of branching

construction exhibited by tropical trees in particular that has led to a quest for of plant architecture.

It is

knowledge

fitting to list

here the

on which this synopsis account is based: Corner 1940; Koriba 1958; Prevost (the article 286) 1967; Halle and Oldeman (architectural models 288) 1970; Oldeman (reiteration 298) 1974; Edelin (architecutral analysis 304) 1977; Halle et al. 1978; Edelin (intercalation 302, and metamorphosis 300) publications

or

may

on which

not incorporate

big as the trunk. There

is

no

it is

located,

and

it

the lesser

all it.

Bough

or limb

correlation between

the words available to describe the architectural of the structure.

For example, both the trunk and a branch of a tree

may

be either monopodial or sympodial

(250) in their make-up.

If

monopodial, the

branch represents a shoot formed by the activity of one single apical meristem (a shoot unit 286). If sympodial, the branch represents a series of shoot units each derived from one apical meristem. This conflict between popular

and botanical detail is discussed under architectural analysis (304). In the

Trees are large and reasonably accessible

branched plants and

lesser stature to that

description

consideration of tree construction or tree

latterly.

It

and the botanical development

to a given set of

but each individual will have a

describe the branching sequence of a plant

a horticultural monstrosity.

is

usually implies an axis of a

particular plant species, but will be flexible within

location

in

terminology (see Tomlinson 1987). 'Branch'

controlled internally, reflecting the form of the

unique array of branches

Acer sp

which presents

constant problems: the use of imprecise

may

branching

280.

aspect of the

trivial

progressive sequences of branching will be

they are

ig.

one

an imprecise word.

All trees of a given species look alike

Contorted branching

is

combined outcome of such activity will lead to the development of a branched organism. The

limits in response to

:

1984, 1990. There

description of branching patterns

intervening sections, loose popular terminology

employed with qualification where necessary avoid ambiguity.

to

is

Plant branch construction: introduction

281

10

mm

.

I

28.

Cory/us avellana, a natural bonsai

Plant branch construction: constructional units

>82

A

plant grows by the progressive accumulation of

similar units;

it is

not, like

most animals, a

fixed

shape that simply enlarges. In the study of plant developmental construction, a number of 'constructional units' real and theoretical, have ig.

282. Piper bicolor

been described and each has

letamers, internode plus node, of the ertical re

monopodial

axis; lateral

branches

sympodial and composed of series of

irticles'

(286, 290b) This species has a

zinged stem (120).

upon the nature

uses depending

its

of morphological investigation

to be undertaken.

A

selection of such units

is

here (282, 284); the two most appropriate

listed

to tree architecture, the article

and the

more

architectural unit, being considered in detail

elsewhere (286 and 304, respectively).

A

complex structure can be more readily understood if it is broken down into manageable components which can be counted and their turnover in numerical terms monitored.

A.

Metamer

A metamer

is

(also called a

phytomer)

a repeated constructional unit,

consisting of a node plus the leaf at that node,

and

its

subtended bud

internode (283a-c).

deemed distal to

if

present, plus a portion of

A metamer may

to include the internode it,

thus be

proximal to

it

or

The plant is a adjacent metamers

or a portion of each.

collection of such units,

possibly having similar or distinctly different

morphological features

(e.g. scale leaf

followed by foliage leaf

metamer

metamer

in Philodendron

10) (White 1984). Disruption of such a sequence will result in

an abnormal plant (270;

Groenendael 1985). B.

A

Phyton

phyton is a unit of construction representing a leaf and its node of insertion plus that portion of

Plant branch construction: constructional units stem proximal has

its

node into which the leaf e). Such a

to the

vascular connections (283d,

segment of stem may or may not be readily identifiable by anatomical analysis. Even if it does have an identifiable anatomical reality, the concept is of dubious practical usefulness. Pipe stem model

C.

The

pipe stem model (Shinozaki

et al.

1964)

envisages a plant, such as a tree, to consist of a

photosynthetic array of leaves supported and served by the trunk and branches (28 3f). Quantitatively a relationship the

amount

is

found between

(fresh or dry weight) of leaf

above a

given horizontal plane, and the total cross-

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all stems and branches at that Thus the plant is seen, in terms, to consist of an assemblage of

sectional area of

plane (28 3f, theoretical

O

g).

unit pipes each supporting a unit quantity of

photosynthetic material. The same analysis can be applied to a stand of vegetation (283h).

(e)

(e)

(Continued on page 284.)

Tm

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