364 Introduction to Botany. 



tion than the orders or families, these being grouped into 

 sub-classes, these into classes, and the classes into sub- 

 kingdoms, which finally are comprised under the vegetable 

 kingdom. 



233. Best Evidence of Relationship. — It is evident that 

 those structures which are apt to vary considerably under 

 changed environment, in the lifetime of a single individual, 

 do not furnish good evidence as to relationships. Thus, 

 individuals of Heliantheiinim vidgare, which are known to 

 be from the same stock and consequently of the same 

 species, exhibit the different forms shown in Fig. 191 

 when grown at different altitudes. It is seen that the size 

 and habit of the plant are greatly altered, while the char- 

 acter of the flowers is quite the same. Many instances 

 could be brought forward to show that the vegetative parts, 

 ■ — that is, those parts which are actively concerned in the 

 life of the individual, — are much more unstable under 

 changed environment than the reproductive parts which do 

 not contribute toward the maintenance of the individual, 

 but are only concerned with the continuance of the species. 

 It is because of the greater fixity of character of the flowers, 

 seeds, and fruits, that chief reliance is to be placed on them 

 in determining relationships. 



