COLOR 189 



outer walls act as lenses in directing all rays 

 of light, which strike the surface at any angle, 

 into the interior, and in some instances actu- 

 ally focusses them upon the chloroplasts. 

 Such an arrangement is to be found chiefly in 

 plants native to moist climates, and gener- 

 ally growing in diffuse light. Oxalis aceto- 

 sella, Cissus discolor, Fucshia triphylla, Mar- 

 anta zevHna, and some begonias are exam- 

 ples showing this adaptation. 



A plant or even a single leaf may exhibit 

 colors due to several causes. Thus the leaf 

 of Begonia falcata has silvery areas of the 

 usual structure, brownish green patches in 

 which the epidermal cells of the upper side are 

 outwardly convex, and those of the lower side 

 contain anthocyan. Arrangements of this 

 character are most frequent in the foliage of 

 tropical plants. The contents of the foregoing 

 paper may be briefly summarized in the fol- 

 lowing paragraphs. 



Colors may serve as an attractive or guid- 

 ing device to lure animals to flowers or away 

 from them. Physiological causes have played Conclusions 

 the principal part in the development of pig- 

 mented regions, and this development may 

 have been modified by the selective power of 

 animals to some extent. The color sense is 

 lacking in some pollen carrying insects, and 

 when present has been acquired in a compar- 



