INTRODUCTION. 3 



case of a leaf and a root, two regions of the body doing 

 different kinds of work. 



5. Plant organs. — These regions of the plant body thns 

 set apart for special purposes are called organ*. The sim- 

 plest of plants, therefore, do not have distinct organs, 

 while the complex plants may have several kinds of organs. 

 All plants are not either very simple or very complex, but 

 beginning with the simplest plants one may pass to others 

 not quite so simple, then to others more complex, and so 

 on gradually until the most complex forms are reached. 

 This process of becoming more and more complex is known 

 as di fferentiation^ which simply means the setting apart of 

 different regions of the body to do different kinds of work. 

 The advantage of this to the plant becomes plain by using 

 the common illustration of the difference between a tribe 

 of savages and a civilized community. The savages all do 

 the same things, and each savage does everything. In the 

 civilized community some of the members are farmers, 

 others bakers, others tailors, others butchers, etc. This is 

 what is known as " division of labor," and one great advan- 

 tage it has is that every kind of work is better done. Dif- 

 ferentiation of organs in a plant means to the plant just 

 what division of labor means to the community ; it results 

 in more work, and better work, and new kinds of work. 

 The very simple plant resembles the savage tribe, the com- 

 plex plant resembles the civilized community. It must be 

 understood, however, that in the case of plants the differ- 

 entiation referred to is one of organs and not of individuals. 

 6. Plant functions. — Whether plants have many organs, 

 or few organs, or no organs, it should be remembered that 

 they are all at work, and are all doing the same essential 

 things. Although many different kinds of work are being 

 carried on by plants, they may all be put under two heads, 

 nutrition and reproduction. Every plant, whether simple 

 or complex, must care for two things : (1) its own support 

 (nutrition), and (2) the production of other plants like 



