FOLIA GE LEA VES. 



407 



should be understood that the pattern is made during the growth 

 of the leaves. 



778. The tree pattern. — Mosaics are often formed by the 

 exterior foUage on a tree, though they are rarely so regular as 

 some of those mentioned above. Still it is common to see in some 

 trees with drooping limbs like the elm, beautiful and large mo- 

 saics. The weeping elm sometimes forms a very close and 

 quite even pattern over the entire outer surface. In most trees 

 the leaf arrangement is not such as to form large patterns, but 

 is more or less open. While the conifers do not form mosaics 

 there are many interesting exampiles of grouping of foliage on 

 branch s^'Stems into broadly expanded areas, as seen in the 

 branches of white pine trees, especially in the edge of a wood, 

 or as seen in the arbor vita". 



OTHER PATTERNS. 



779. Imbricate pattern of short stems. — This pattern is quite 

 common, and ditTers from the rosette in that the leaves are dis- 

 tributed further apart on 



the stem so that the cen- 

 tral ones are consider- 

 ably higher up than in 

 the mosaic. The lower 

 petioles are longer, as in 

 the rosette, so that the 

 outer lower leaves ex- 

 tend further out. Some 

 begonias show fine im- 

 bricate patterns. 



780. Spiral patterns. 

 — They are very common 

 on stems of the cylindrical 



Fig. 445. 

 Imbricate pattern of lea\'es; Begonia. 



type, which are unljranched, or but little branched. The sun- 

 flower, mullein, chrysantheinum, as it is grown in greenhouses, the 

 Easter lily, etc., are examples. The spiral arrangement of the 

 leaves provides that each successive leaf on the stem, as one ascends 

 the stem, is a little to one side .so that it does not cast shade on the 



