96 



LEAF ARRANGEMENT AND MOVEMENTS 



When this is sufficiently regular, usually with the spaces between 

 the leaves a good deal smaller than the areas of the leaves them- 

 selves, it is called a leaf mosaic (Fig. 106). Many of the most 

 interesting leaf groups of this sort, as in the figure above men- 

 tioned, are found in the rosettes of the so-called root leaves of 

 plants. Good examples of these are the dandelion, chicory, fall 

 dandelion, thistle, hawkweed, Pyrola, and plantain. The leaves 

 of these plants are kept from shading each other, sometimes by 



s 



FIG. 104. Opposite leaves of Deutzia l (from the same shrub as Fig. 105) 



as arranged on a horizontal branch 



the narrowness of the leaves and sometimes by the lengthening 

 of the leafstalks of the lower ones. 



113. Much-divided leaves. Not infrequently leaves are cut 

 into slender, fringe-like divisions, as in the carrot, tansy, south- 

 ernwood, wormwood, yarrow, dog fennel, cypress vine, and many 

 other common plants. This kind of leaf seems to be adapted to 

 offer considerable surface to the sun without cutting off too 

 much light from other leaves underneath. Such a leaf is in 

 much less danger of being torn by severe winds than are broader 

 ones with undivided margins. The same purposes are served by 



1 Deutzia crenata. 



