THE PLANT BODY 



^Corolla 



75 



FIG. 40. The Floral parts of the Alpine Azalea (Loiseleuria). Collectively 

 the sepals constitute the calyx, and the petals, the corolla. The pistil repre- 

 sents several united carpels. (From Bergen and Caldwell, after Miiller.) 



parts that fit plants for different modes of life, to obtain 

 some insight into the tissue organization, or HISTOLOGY, of a 

 typical plant. 



B. HISTOLOGY 



As we have seen, the functions of organisms are performed 

 by their protoplasm which constitutes the structural units, or 

 cells. The cells, when specialized for a particular duty in 

 the economy of the organism, are usually associated in more 

 or less homogeneous groups, or tissues. Tissues, in turn, are 

 grouped to form tissue systems and organs; that is, major 

 divisions of the body which allow the tissues and, therefore, 

 the cells devoted to a special function to play their part under 

 the most suitable relations to internal or external conditions. 

 It is important, however, as we resolve the individual plant 

 (or animal) into its component cells, tissues, or organs, not to 

 lose sight of the fact that these parts are all at work for the 

 good of either the individual or the race. The many dif- 

 ferent kinds of work which are being carried on by the organ- 

 ism, whether it is simple or complex, must provide in the 

 final analysis for two things: the support or nutrition of the 



