88 



BOTANY 



PART I 



metres (to more than 50 cm.) from this. It is not of course so active 

 in the successively distant zones. The elongation may, on the other 



hand, be so slight that the mature 

 leaves of the shoot adjoin one 

 another without leaving any free 

 surface of stem between them. 

 As a rule, however, its amount and 

 distribution is such that the inser- 

 tions of the leaves become separated 

 by bare regions of stem (Fig. 1 1 5). 

 These are known as INTERNODES, 

 while the transverse zones of the 

 stem where the leaves are inserted 

 are the NODES. The growth in 

 length is much less in the nodes 



internodes. In the 

 often limited to a 



FIG. 103. Transverse section of a bud of Populus than in the 



nigra. fc, Bud -scales showing imbricated latter it is 

 aestivation [vernation] ; I, foliage leaves ,. 



with involute J vernation [ptyxi*] ; ., each leaf naiTOW ZOne, for example at the 



has two stipules, (x 15. After STRASBURGER.) base of the internode in the 



Grasses. There are then a number 



of zones of intercalary growth in the stem separated by fully -grown 

 regions. The nodes may be swollen (cf. Labiatae). 



In the aerial shoots the internodes are usually thin, while they are frequently 

 very thick in subterranean shoots. 



The length of successive internodes of an axis exhibits a certain regularity. 

 Usually it increases on ascending a main axis and then diminishes. 



Leaf Arrangement ( 5G ). The distribution or arrangement of the 

 leaves is very characteristic of shoots, and exhibits great variety. 

 One or a number of leaves may be borne at each node. When there 

 are several leaves they form a WHORL and are termed the members of 

 the whorl, while the leaf arrangement is spoken of as VERTICILLATE. 

 When there is only one leaf at each node the arrangement is 

 ALTERNATE. A very remarkable and peculiar regularity is exhibited 

 by the arrangement of leaves on all sides of erect shoots ; it is often 

 at once evident when the growing point is looked at from above 

 (Figs. 99, 104). The youngest leaf-rudiments adjoin the older ones 

 in such a way as to best utilise the available space. The relations of 

 position are best shown when they are plotted diagrammatically on a 

 ground-plan. The position of the leaves is represented in the diagram, 

 which is of a plane at right angles to the axis of the stem, as if the 

 latter were conical and viewed from the tip; it is thus possible to 

 indicate a higher position on the stem by a more internal position in 

 the plan. Such ground-plans of leaf arrangements are called DIAGRAMS 

 (Fig. 105). The centre corresponds to the apex of the stem; the 

 leaves nearest to this are the youngest or uppermost, and those 



