404 ORDERS.—SUB-ORDERS.—CLASSES. 
we shall find that some of them also resemble each other more 
than they do other genera. Thus, Mustards, Turnips, Radishes, 
and Cabbages have a strong common resemblance, while they 
are unlike Strawberries and Brambles; and even less so to 
Hazels, Oaks, and Beeches; and still more unlike Larches, 
Pines, Firs, and Cedars. Proceeding in this way throughout 
the Vegetable Kingdom, we collect together allied genera, and 
form them into groups of a higher order called Orders or Natural 
Orders ; hence, while genera are collections of related species, 
orders are collections of allied genera. Thus, Turnips, Radishes, 
and Cabbages, all belong to different genera, but they agree in 
their general structure, and are hence included in the order 
Crucifere ; while Strawberries, Brambles, Roses, Apples, and 
Plums, are all different genera, but from the general resem- 
blance they bear to each other in their structure, they are placed 
in one order, called Rosacex. Again : Oaks, Beeches, and Hazels 
are different genera, but they belong to one order; also the 
Pines and Cedars are different genera, but as the fruit of them 
all is a cone, they are grouped together in one order, which is 
termed the Conifere. 
We find also that certain genera of an order, like certain 
species of a genus, have a more striking resemblance to each 
other than to other genera of the same order; hence such are 
grouped together into what are called Sub-orders. Thus the 
Chicory, Dandelion, Sow-thistle, Lettuce, Thistle, Burdock, and 
Chamomile, all belong to the same order, but there is a greater 
resemblance in the Chicory, Dandelion, Sow-thistle and Lettuce 
to each other than to the remaining genera. Hence, while all 
the above genera belong to the order Composite, they are at the 
same time placed in two different sub-orders. Thus, one sub- 
order, called the Liguliflore, includes the Chicory, Dandelion, 
Sow-thistle, and Lettuce ; and the other sub-order, the Tubuli- 
flore, that of the Thistle, Burdock, and Chamomile. In like 
manner, while we find the Plum, Strawberry, Raspberry, Rose, 
and Apple, all belonging to the same order Rosacex, some of 
them have more resemblance to each other than to others. 
Thus, the Plum has a drupaceous fruit, and is therefore placed in 
a distinct sub-order, which is called Drupacezx ; the Strawberry, 
Raspberry, and Rose are much more like each other than they 
are to the Plum or Apple, hence they are put in a sub-order 
called Rosex ; while the Apple, from the character of its fruit, 
is placed in a sub-order termed Pomee. 
It is also found convenient to subdivide sub-orders into 
Tribes, Sub-tribes, &c., by collecting together into groups cer- 
tain very nearly allied genera, but it is not necessary for us to 
illustrate such divisions further, as the principles upon which 
they depend have been now sufficiently treated of. , 
4, CiassEs.—By a class, we understand a group of orders 
possessing some very important structural characters in common. 
