EXPOSURE TO LIGHT 241 
Figure 222. Many trees as well as many herbaceous plants, 
such as Cotton, Clover, Alfalfa, Tomatoes, Potatoes, Buckwheat, 
and Flax, have the alternate arrangement of leaves. In the 
opposite arrangement two leaves appear at each node on opposite 
sides of the stem, and neighboring 
pairs are set more or less at right 
angles to each other, so that as one 
looks down from above each pair 
of leaves alternates in position with 
the pair above and with the pair 
below it as shown in Figure 223. 
The opposite arrangement is also 
common among both woody and 
herbaceous plants. In the whorled 
arrangement more than two leaves Tio. 99%, — Dandelion “wiewed 
occur at a node, as illustrated in from above. The leaves form «a 
Figure 224. In this arrangement rosette and the lower leaves are 
the leaves are also so placed as to ™uch longer than the upper ones. 
shade each other as little as possible. HEE Steven 
In plants, like the Dandelion and Plantain, which have very short 
stems bearing many leaves, the leaves form a mat, called a rosette, 
on the surface of the 
ground. It is readily seen 
that leaves so closely 
crowded as they are in the 
rosette must shade each 
other considerably, but 
they have the advantage 
of being exposed less than 
those on clongated stems 
to the loss of water by 
transpiration. In the 
rosette much shading is 
eliminated by a difference 
in length of petioles, for the outer and under leaves of the rosette 
have longer petioles which push their blades beyond those of the 
upper leaves, and in this way they escape the shade of the leaves 
above. This feature is noticeable in the rosette of the Dandelion 
shown in Figure 225. Another arrangement of leaves which is 
favorable to light exposure is called a leaf mosaic, being so named 
Fig. 226. — Nasturtiums showing mosaic 
arrangement of leaves. 
