BUDS AND LEAF ARRANGEMENT. 49 
above another. If, in the latter case, the upper one develops, an 
extra-axillary branch is the result. Adventitious buds may also 
occur, which observe no regularity in their place or time of 
development. Most of the shoots on old tree-trunks belong to 
this category, and they may also be produced on some roots, or 
even on leaves. An example of the last is seen in begonias. A 
leaf of one of these plants if fixed in the earth will develop roots 
from the end of its stalk, and buds in various places. 
The terms prefoliation and vernation are applied to the ways in 
which leaves are packed in the buds. The individual leaves are 
disposed in various manners, and their mutual relation is different 
in different cases.1 We now come to the arrangement of mature 
leaves on the stem. This partly depends on the length of the 
internodes (p. 24) and partly on the size of the leaves. But 
apart from this, it is found that, in a given plant, the leaves are 
always attached or inserted at points which bear a definite rela- 
tion to one another, which relation may be expressed numerically. 
Arrangement of the leaves, in this sense, is known as phyllotaxis. 
A node may bear two or more leaves, when the term whorled is 
used, or else only one, which fact is denoted by the words scattered 
or alternate. In the simplest case a whorl consists of two mem- 
bers, as in dead nettle, pink, horse-chestnut, and lilac Such 
opposite leaves are generally decussate, 1.e., successive pairs alter- 
nate with one another. This is very well seen in the dead nettle, 
and even a cursory examination will show that the leaves here 
form four lines, ranks or orthostichies. along the stem, one ortho- 
stichy corresponding to each of its four flat sides. Angled and 
ridged stems frequently exhibit a relation of this kind. A whorl 
in other cases may consist of three or more members, and here 
also the leaves are respectively above and below the spaces between 
the members of the whorl below and the whorl above. Transi- 
tions between the whorled and alternate arrangement are com- 
monly met with. For example, the rapidly-growing stems of the 
Jerusalem artichoke (Helianthus tuberosus) bear opposite leaves 
below and alternate ones above, the two ways of arrangement 
gradually passing into each other. And in all, or nearly all 
1 The following are the chief terms applied to the ways in which individual 
leaves are folded or rolled in leaf (and flower) buds :— 
(1.) When folded: plated (in some palmately-veined leaves), when folded 
like a fan; conduplicate, doubled up longitudinally, the upper surface internal ; 
inflexed, the upper part bent down on lower. 
(2.) When rolled: convolute, in a continuous roll, upper side being internal, 
and one margin forming centre of roll ; imvolute, both margins rolled inwards ; 
revolute, both margins rolled outwards ; circinate, rolled from the tip down- 
wards, like a crozier; crumpled, explains itself. Compare also footnote, 
p. 84. 
D 
