6 5 2 



FAMILIES OF ANGIOSPERMS. 



flower are frequently in fives; the vascular bundles of the stem 

 are generally open and arranged in rings around the stem, as shown 

 in the cross-section of the oak (fig. 539). There are exceptions 

 to all the above characters, and the sum of the characters must 

 be considered, just as in the case of the monocotyledons. 



19 



r ni- 



A Fig. 539. 



A. Cross-section of the stem of an oak tree thirty-seven years old, showing the 

 annual rings, rm, the medullary rays; m, the pith (medulla). B. Cross-section 

 of the stem of a palm tree, showing the scattered bundles. 



1143. Taxonomy. This grouping of plants into species, 

 genera, families, etc., according to characters and relationships 

 is classification, or taxonomy. 



To take Trillium grandiflorum for example, its position in 

 the system, if all the principal subdivisions should be included 

 in the outline, would be indicated as follows: 

 Group, Angiosperms. 

 Class, Monocotyledones. 

 Order, Liliales. 

 Family, Liliaceae. 

 Genus, Trillium. 



Species, grandiflorum. 



In the same way the position of the toothwort would be indi- 

 cated as follows: 



Group, Angiosperms. 

 Class, Dicotyledones. 

 Order, Papaverales. 

 Family, Cruciferae. 

 Genus, Dentaria. 

 Species, diphylla. 



