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36

I

Leaf morphology: ptyxis, folding of individual leaves

Developing leaves are often confined within a

bud (264), and

protective structure, a

at this

stage will quite possibly have acquired less their final

shape (mostly by

more

or

cell

multiplication) but not reached their final size

(mostly due to

cell

upon the number,

enlargement). Depending size,

and complexity of the

leaves in the bud, they are likely to be variously

manner of folding being consistent for any given species. The phenomenon of leaf packing is referred to by a variety of terms. The folded, the

contortion of a single leaf

is

is

Drosophyllum lusitanicum

insectivorous plant with circinate ptyxis. Unusual

in

the leaves are rolled outwards rather than inwards as

in

Fig.

that

37e

called ptyxis (from

modes

the Greek for folding), the various

packing of leaves together

Fig. 36a.

An

of

referred to as

vernation (or prefoliation 38). The packing of perianth segments in a flower bud

is

very similar

to that of vegetative leaves in a vegetative

and The

bud

termed aestivation or prefloration (148). different forms of ptyxis are frequently of is

diagnostic value in identifying a plant

and as

such have acquired an extensive range of terminology. The most

common

terms are

illustrated here (37) in three-dimensional

diagrams which convey more information than an over-simplified written description. The individual leaflets of a

compound

leaf

may

be

one manner, the leaf as a whole showing an alternative arrangement. The folding of the leaves of palms is particularly elaborate and is a function of their unique mode of development (92). An extensive discussion of folded in

ptyxis occurs in Cullen (1978).

Fig. 36b.

Nelumbo nucifera

Peltate leaves (88) with involute folding (37b)

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[adrian d bell] plant form an illustrated guide (bookfi org)  

[adrian d bell] plant form an illustrated guide (bookfi org)