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 phi/llota.vis. 

 A node may bear two or more leaves, when the term wliorled 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, i.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 wliorled and alternate arrangement are com- 

 monly met with. For example, the rapidly- growing stems of the 

 Jerusalem artichoke (Helianthus tuberosns) 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 : plaited (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 ; involute, 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. 



