FOLIAGE LEAVES: THE LIGHT-RELATIOX. 9 



and not too much. The danger from too much light is 

 not the same in the case of all leaves, even on the same 

 plant, for some are more shaded than others. Leaves also 

 have a way of protecting themselves from too intense light 

 by their structure, rather than by a change in their posi- 

 tion. It is evident, therefore, that the exact position which 

 any particular leaf holds in relation to light depends upon 

 many circumstances, and cannot be covered by a general 

 rule, except that it seeks to get all the light it can without 

 danger. 



13. Fixed position. — Leaves differ very much in the power 

 of adjusting their position to the direction of the light. 



Fig. 2. The day and night positions of the leaves of a member (AmUHa) of the pea 

 family. — After Strasbvbger. 



Most leaves when fully grown are in a fixed position and 

 cannot change it, however unfavorable it may prove to be, 

 except as they are blown about. Such leaves are said to 

 have fixed light positions. This position is determined by 

 the light conditions that prevailed while the leaf was grow- 

 ing and able to adjust itself. If these conditions continue, 

 the resulting fixed position represents the best one that can 

 be secured under the circumstances. The leaf may not 

 receive the rays of light directly throughout the whole 

 period of daylight, but its fixed position is such that it 

 probably receives more light than it would in any other 

 position that it could secure. 



