404 



RELATION TO ENVIRONMENT. 



V. Leaf Patterns. 



MOSAICS, OR CLOSE PATTERNS. 



774. \Miere the leaves of a plant, or a portion of a plant, are 

 approximate and arranged in the form of a pattern, the leaves 

 fitting together to form a more or less even and continuous sur- 

 face, such patterns are sometimes termed "mosaics," since the 

 relation of leaves to one another is roughly like the relation of 

 the pieces of a mosaic. A good illustration of a mosaic is pre- 

 sented bv a greenhouse plant Fittonia (iig. 44i). The stems 



ig- 441- 



Fittonia showing leaves arranged to form compact mosaic. The netted vena- 

 tion of the leaf is very distinctly shown in this plant. (Photo by the Author.) 



are prostrate and the erect branches quite short, but it may 

 have quite a wide .s)-steni bv the spreading of the runners; the 

 branches of such a length that tlie leaves borne near the tips all 

 fit together forming a broad surface of leaves so closelv fitted 

 together often that the stems cannot ])e seen. The ad\'antage 

 of a mosaic over a sei)aratc disposition of leaves at somewhat 

 different levels is that the leaves do not shade one another. Were 

 all the light ra}'s coming down at riglit angles to the leaves, there 

 would not Ije any shading of the lower ones, but the oblique 

 ravs of light would he cut off from many of the lea\'es. In the 

 case of a mosaic all the ra\'s of h'glil plav upmi all llic leaves. 

 Some (if the mosai(S wliich can be iibscr\i'i| arc as follcnvs: 



