LEAVES 



by one-thiid of the circumference. The relative disposi- 

 tion of the leaves at the different nodes is equally regular. 

 In some cases the leaves at the successive nodes are 

 exactly above one another (superposed), so that there are 

 just as many rows of leaves along the stem (longitudinal 

 rows) as there are leaves at each node — for instance, 

 there will be two longitudinal rows of leaves if there are 

 two leaves at each node. But on other stems with whorled 

 leaves, the leaves at one node stand above the gaps 

 midway between the leaves of the next lower or next 



higher node ; thus the leaves 

 at the successive nodes exactly 

 alternate with one another. 

 Consequently, the leaves of 

 every second node will stand 

 above one another. In this 

 case there will be exactly twice 

 as many Idngitudinal rows of 

 leaves as there are leaves at 

 a single node. For example, 

 the Dead Nettle, the Chickweed 

 (fig. 43), have two leaves at 

 each node, but those at the 

 successive nodes alternate so 

 that there are four rows along 

 the stems. 



Alternate or Spiral (Acyclic) 

 Leaves. — When only one leaf 

 stands at each node (fig. 12), 

 the leaves are arranged in 

 spirals, and not in circles or 

 whorls. They form rows, and 

 are ranged one above the other 

 along the stem, as is the case 

 with whorled leaves. Each leaf 

 is separated from the one at 

 the next node, either below or 

 '°f Hazel with J leaf- above it, not Only by a vari- 

 able distance along the stem, 

 but also by a certain invariable angular distance round the 

 stem. For example, on Grass-stems and most Hazel-stems 



Fig. iz. — Erect shoot 

 arrangement. 



