6. ARRANGEMENT OF LATERAL MEMBERS. 11 



nected with the acropetal order of their development ; and since 

 the arrangement of the lateral shoots depends on that of the leaves, 

 the same laws determine the arrangement of both these sets 

 of members which apply generally to all acropetally developed 

 members of plants. These laws are most conspicuously exhibited 

 in the arrangement of the leaves, and they will be fully discussed 

 with reference to these members only. 



The leaves are developed in very close apposition at the growing- 

 point of the stem. The portions of the stem, termed internodes, 

 which lie between the individual leaves may either remain quite 

 short, as in the case of the rosette of leaves of the Plantain and of 

 the Houseleek, of the fascicled leaves of the Larch, and in most 

 flowers ; or they may undergo a considerable elongation so that the 

 leaves become widely separated. The boundaries of the iuternodes 

 the places, that is, at which the leaves are inserted termed nodes, 

 are sometimes prominently developed, more particularly when the 

 leaves are arranged in whorls, e.g. Labiatae, or when they ensheath 

 the stem. The portion of the surface or the stem from which the 

 leaf arises is the insertion of the leaf, and its organic centre is 

 called the point of insertion. 



So long as the internodes have not begun to elongate, and the 

 leaves are still folded together so as to cover the apex of the 

 stem, the growing end of each shoot is known as a bud. The bud 

 which lies at the apex of a shoot, the lower portion of which has 

 already undergone elongation, is a terminal bud ; the lateral buds 

 are the early stages of shoots developed laterally upon a growing 

 main shoot, which often remain in this condition for a considerable 

 time. The arrangement of the lateral buds, and consequently that 

 of the branches which are developed from them, is closely related 

 to that of the leaves ; thus whilst in the Pteridophyta the bud 

 may be developed immediately below or by the side of a leaf, in the 

 Phanerogams it is nearly always developed in the axil of a leaf, 

 that is to say, in the angle made by a leaf with the internode 

 above its insertion. In the latter case the buds make their ap- 

 pearance at the first formation of the leaves (Fig. 3 kn). As a 

 general rule, they are developed in the axil of every leaf, typical 

 exceptions being the leaves that form the flower, and those of 

 many of the Conifers. In some cases certain of the internodes do 

 not elongate, and therefore the leaves, which have been really 

 developed singly, or their axillary buds, appear to have been 

 developed at the same level on the stem, thus forming a spurious 



