ORDERS. 117 



characters of these, botanists have bestowed the highest degree 

 of attention, and tlic student's progress will depend chiefly upon 

 his acquaintance with them. 



356. Orders are formed by associating together those genera 

 which are tlie most nearly allied to each other, or to some one 

 genus previously assumed as the type. Therefore, as the spe- 

 cies form genei-a, so genera form orders. 



357. In systematic works, the orders are also associated on 

 natural principles into alliances, groups, &c., which are inter- 

 mediate between these and the sub-classes, and are designated 

 numerically, thus, group 1st, group 2d, &c., or by names derived 

 from a leading order. 



358. Li regard to their extent, the orders differ very widely, 

 some consisting of a single genus, as San^aceniaceae, while 

 others comprehend hundreds of genera, as Composita?. For 

 convenience' sake the larger orders are broken up into sub- 

 orders, or tribes. 



359. The Natm-al System, with its classes and suborduiate 

 divisions, may be exhibited in one view ; 



The Vegetable Kingdom is separated 



1st, into Grand Divisions and Subdivisions. 



2nd, " Classes. 



3d, " Sub-classes, AUiances, and Groups. 



4th, " Orders and Sub-orders. 



5th, " Genera and Sub-genera. 



6th, " Species and Varieties, and 



7th, " Individuals. 



