160 



BOTANY: PRINCIPLES AND PROBLEMS 



structure of parts may be so modified that as small a surface as 

 possible is exposed to light when it becomes very bright. In some 



Fig. 78. — Etiolation. The two bean seedlings are of the same age but the one 

 at the right was grown under normal illumination, the one at the left, in darkness. 

 Note the longer internodes, the paler color, and the poorer leaf-development of 

 the darkened plant. 



species, for example, the broad surface of the blade is exposed to 

 light of moderate intensity but only the edge to very bright 

 illumination. 



