viii. PRE FA CE. 



obvious to the practiced eye, of the experienced col- 

 lector. 



Among these is the particular thing which I wish 

 to direct attention to here, viz. : the disarrangement 

 of the species, in the genera. It will be observed, 

 that while the genera have been arranged in their 

 proper natural order, the species are often grouped, 

 in the text, quite otherwise. The reason is, I have 

 taken those species, in genera which contain several, 

 for treatment first, which, on account of their common- 

 ness, or peculiar habitat or appearance, could be most 

 easily and certainly identified. From these, I have, 

 proceeded step by step, to the more difficult plants. 



Then again, I have often found it convenient, to 

 group certain species together, for the advantage of 

 comparison, in the description, which do not always 

 naturally belong together. You will therefore under- 

 stand, that while the orders and genera, follow their 

 natural grouping, in the text, the species in the 

 genera cannot be depended upon to do so, in most 



cases. 



I must add a single remark further, on this general 



subject. While the several sub-classes, the Green, 



