PHILOSOPHICAL SOCIETY OF WASHINGTON. 



93 



Comparison of Genera. 



The whole number of genera in the flora of the Eastern United 

 States is 1065. That of the Flora Columbiana, as already stated 

 is 527. This is over 49 per cent., a much larger proportion than 

 was shown by a comparison of the species. A comparison of the 

 genera by classes, gives the following results : 



The percentages here range from 33 in the Gymnosperms to 57 in 

 the Monocotyledons, averaging between 49 and 50, whereas in the 

 similar comparisons for species they ranged from 22 in the Crypto- 

 gams to 36 in the Monoclilamxjdeoz. This result was to be expected 

 since as the groups increase, the number represented in any local 

 flora should be proportionally larger. For example, 116 orders out 

 of the 156 are represented here, which is upwards of 74 per cent. 



Comparison of Large Orders. 



It will be interesting to compare in a manner similar to the fore- 

 going, the number of species in several of the largest orders. For 

 this purpose we may use the same orders mentioned a few pages 

 back as the richest in species of any belonging to this flora. The 

 comparison may then be shown as follows : 



