HOMOLOGIES 327 
just as the morphological study of plants forms the scientific 
basis of systematic botany. To a certain extent the concep- 
tions involved are necessarily abstract, or, so to say, dia- 
grammatic; for the parts of plants are thus viewed only in 
one aspect, and for the sake of being able to think of them 
Fig. 281.—Diagram of a typical flowering plant showing the principal 
parts and their homologies. Root-members are black; stem-members, 
shaded with lines running lengthwise; leaf-members, shaded with lines 
across; and sac-members, unshaded. (Original.) 
simply many facts are deliberately left out of account. The 
conclusions reached nevertheless may be true so far as they go, 
and are valuable aids to fuller knowledge; but the student 
should remember that natural objects are never diagram- 
matic and that Nature does not draw the sharp lines of dis- 
tinction which we may find it useful to assume. 
