TEXTBOOK OF BOTANY 



Fig. 4. Lichens growing on a vertical rock face. Photo by C. H. Jones. 



larger animals in so many ways that they not only are readily distin- 

 guished but are commonly thought to be quite unrelated. To suggest that 

 horses and trees have certain characteristics in common may seem ab- 

 surd. But students of plant and animal life have found that many of the 

 processes in plants and animals are either identical or essentially similar 

 if the basis of comparison is limited to certain fundamental features. 

 Among the microscopic organisms are many that resemble animals quite 

 as much as they resemble plants, and it would be futile to try to classify 

 them strictly in either category. 



The biological sciences. Knowledge that pertains to plants or animals 

 or to both is called biology. The range of biological information that has 

 accumulated through the centuries — but more especially during the last 

 hundred years — is now so extensive that no one person is entitled to be 



