ACTION OF FORCES ON ORGANISMS. 57 



"Kohl has proved by experiment that the leaves 

 of Tropceohim plants display different properties 

 according as they are 'grown in a moist or a dry 

 atmosphere, the other conditions of growth being 

 the same. The leaves grown in dry air are provided 

 with a thick cuticle, and vmder the epidermis is a 

 strong growth of collenchym tissue ; while the leaves 

 raised in moist air show a thin cuticle and no 

 collenchym. 



"According to StahVs observations, the anatomical 

 structure of the leaves of some plants shows a great 

 difference as a result of having developed in strong 

 light or in shadow. The assimilative parenchym of 

 beech leaves which grow in sunlight, for example, 

 consist almost entirely of palisade cells, while the 

 palisade cell in the leaves grown in shadow are very 

 few ; a circumstance which, though it cannot be 

 discussed here, is of great significance for the 

 function of the leaves. Heinreicher also gives 

 examples from which it appears that the condi- 

 tions of light have a decided influence upon the 

 anatomical structure of the leaves of different indi- 

 viduals of the same species of plant. The newer 

 botanical literature has acquainted us generally with 

 numerous facts concerning the relations between the 

 morphological and anatomical peculiarities of plants, 

 and the climatic influences or other conditions of life 

 to which the organisms are exposed." 



