n. OEBERS AND GENEBA. 81 



various instances. And in truth they are only varied re- 

 combinations, substituted for the subdivisions of other 

 systematists. 



Examj)les may give a better conception of what is here 

 intended, in saying that the orders of botanical systema- 

 tists are not formed on uniform ^Drinciples, and are not 

 sufficiently co-equivalents to meet the wants of the Phyto- 

 geographer, by giving precision and clearness to his com- 

 parisons founded upon such groups. With this object, 

 some examples of non-uniformity and non- equivalence of 

 orders may be cited here, and selected by preference from 

 those represented in Britain. In the following series the 

 names which are printed on the same line may be consi- 

 dered to represent nearly equivalent groups, and such as 

 are formed on a somewhat uniform principle. But the 

 names placed in different lines, — especially in contrasting 

 those placed in different lines not immediately succeeding 

 each other, — certainly represent groups which have not 

 been formed on uniform principles, and which are not 

 equivalents of each other. 



1. Filices. Gramina. Cyperoides. 



2. Compositse. Cruciferse. Umbelliferge. 



3. Eosacese. Ericaceae. Liliacese. 



4. Boraginacese. Primulacese. Gentianaceae. 



5. Gahacese. Valerianacese. Dipsacese. 



6. Pinguiculacese. Plantaginacese. Tyi^haceae. 



7. Ceratophyllaceae. Callitrichaceae. Elatinacese. 



Looking to the three several orders named in the first 

 line, their included plants present decided and conspi- 

 cuous characters, by which the plants of the same order 

 resemble each other, and by which they may be dis- 

 tinguished from the plants of all other orders. The 



