50 THE STORY OF PLANT LIFE 



its phylogeny. These differences of generic value in 

 the case of flowering plants are generally of a higher 

 type than those that distinguish species. They have 

 to do with the floral structure as a rule, a factor which 

 is used throughout the plant kingdom, or at least in 

 the case of Phanerograms,in classifying plants accord- 

 ing to their grades of relationship or main divisions. 



Thus while the plants of the genus Ranunculus 

 agree with those of the genus Adonis in possessing 

 carpels which are arranged in a round or oblong head, 

 the former differs from the latter in having a scale at 

 the base of the petals. The fact that the flowers of 

 Adonis are red in the British species distinguishes 

 the genus in this case from those of plants of the 

 genus Ranunculus^ where the flowers are yellow or 

 white. These two genera are also distinguished (with 

 others) from a second group of plants in the same 

 family (order), by the fact that the carpels are here 

 one-seeded, whereas in Larkspur, for instance, the 

 carpels are many-seeded. 



Several genera are collected together on a similar 

 basis and arranged in a family, or natural order as 

 these are frequently termed, because they each agree 

 in some important character, and may be dis- 

 tinguished from all other families or natural orders 

 in this respect. The order Ranunculacese includes 

 genera in which the plants have generally the 

 stamens distinct and hypogynous, and in which the 

 carpels are also distinct. From the Rosaceae, with 

 which they agree in having the carpels free and 



