THE PINE FAMILY. 155 



Write a brief summary of the particulars in which all the 

 species thus far examined agree. These, with certain 

 features that you have not yet observed, constitute the 

 family characters of the Coniferse. 



RELATIONSHIP. 



From the preceding study it will be easy to understand 

 something of the relationship of plants and the way this is 

 determined by botanists. 



1. Plants that are related to each other show a mutual 



resemblance. This ma}' be observed in 

 a. External features and habits, including form, direc- 

 tion of growth, etc. 

 h. Structure. 



c. Reproduction. 



d. Developmental history. 



e. To some extent, physiological peculiarities. But 



in this respect closely related plants often show 

 great differences. 



In our study of the conifers we have directed our atten- 

 tion chiefly to external features. 



2. Plants exhibit degrees of relationship, those most 



closely related being most alike, while those re- 

 motely related are less alike. 



3. Plants that are related as parents and offspring, 



forming a succession of individuals not to be 

 distinguished from each other by any constant 

 differences, constitute a species. The white pine 

 is one species, the Austrian pine another, and 

 so on. 



4. Closely related species constitute a genus. Thus the 



various species of pines together make up the 



