18 TREES OF THE NORTHERN UNITED STATES 
with the observation of trees, will soon teach the student 
what constitutes a leaf. 
ARRANGEMENT.— There are several different ways in 
which leaves are arranged on trees; the most common 
plan is the alternate ; in this only one leaf occurs 
ata joint or node onthe stem. The next in frequency is 
the opposite, where two leaves opposite each otber 
are found at the node. A very rare arrangement 
among trees, though common in other plants, is the 
whorled, where more than two leaves, regularly ar- 
ranged around the stem, are found at the node. 
When a number of leaves are bundled together,—a plan 
not rare among evergreens,— they are said to be fascicu- 
lated or in fascicles. aaa The term scattered is used 
where alternate leaves are crowded on the stem. This 
plan is also common among evergreens. 
Caution. — In some plants the leaves on the side 
shoots or spurs of a twig are so close together, the inter- 
nodes being so short, that at first sight 
they seem opposite or clustered. In 
such cases, the leaf-scars of the pre- 
ceding years, or the arrangement of 
the branches, is a. better test of the 
true arrange- 
ment of the 
leaves. The 
Fig. 5. ‘twig of Birch 
shown in Fig. 5 has alternate leaves. 
There is one variety of alterna- SN 
tion, called two-ranked, which is 
quite characteristic of certain trees; aS Ue 
Ui 
that is, the leaves are so flattened ee 
1 
T 
out as to be in one plane on the 
opposite sides of the twig (Fig. 6). 
The Elm-trees form good examples Fig. 6. 
aig 
