NEW ZEALAND NATURE-STUDY BOOK 
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VI.—LEAF ARRANGEMENT. 
Arrangement of Leaves on Stem. The level at 
which a leaf grows on a stem is called a node, and the 
distance between two consecutive nodes is known as an 
internode. In some stems two or more leaves are 
attached at the same level i.e. at the same node; the leaf- 
arrangement is thensaid to be whorled, and the group of 
leaves at each node is called a whorl. On other stems 
(e.g. Wallflower) there is only a single leaf at each node, 
when the arrangement is known as spiral. ; 
‘Whorled Arrangement. The leaves, when they 
occur in whorls, are arranged round the stem in a very 
regular manner, the angular distance between each pair of 
adjacent leaves being the same. Thus if there are two 
leaves at a node, they will be found growing on opposite 
sides of the stem as in the Hange-hange (Geniostoma Ligustri- 
folium). When three leaves occur each one is separated from 
the next by one third of the circumference of the steni. 
If the whorl consist of four leaves, they are arranged like 
the four arms of a cross, a quarter of the circumference of 
the stem separating each pair. 
The way in which the leaves are disposed at one node 
relatively to those at successive nodes either above or below 
is equally regular. In some cases they are immediately 
above each other, in which case there are as many longi- 
tudinal rows of leaves as there are leaves at each node, when 
the leaves are said to be superposed. Some of the 
common Ferns will furnish examples. In others each 
leat in one whorl is immediately above a vacant space 
between two leaves in the next lower whorl, and the leaves 
of every alternate node stand exactly over each other, well 
seen in several species of Rata, ¢.g., Pohutukawa and Climbin g 
