ARTIFICIAL TABLE. 235 



dies' -mantle ( Alchemilla), belonging to the Polypetalous 

 subclass of Exogens, have in reality no petals ; Glaux, 

 belonging to the Monopetalous subclass of Exogens, 

 has no petals ; Correa^ belonging to the Polypetalous 

 subclass of Exogens, has a monopetalous corolla ; and 

 so on. No doubt, a Botanist who has had a little 

 experience, overcomes these difficulties easily enough, 

 because he will recognize the plants by the remainder 

 of their structure, and notwithstanding their deviation 

 from the general rule. But, although there exist ex- 

 ceptions to all rules whatsoever, and every person 

 must, therefore, be accustomed to contend with them, 

 whatever the branch of knowledge to which his studies 

 have been directed ; yet it must be confessed, that 

 they are always very embarrassing to a beginner, and 

 should be provided against by the best means that can 

 be devised. Therefore, as my parting gift, and an 

 appropriate conclusion to the correspondence that has 

 passed between us, I send you a key, not only to all 

 the Natural Orders of plants you have yet seen, but also 

 to such others as you are at all likely to meet with. 



It is only necessary for you to know how to use 

 this key, and I confidently expect you will be at once 

 relieved fi'om all future embarrassment, both in dis- 

 tinguishing the orders themselves, and in guarding 

 yourself against errors arising from exceptional cases. 

 I would, indeed, advise you at first to use your key in 

 all cases whatever, whether of doubt or not ; for you 

 will find it give you a habit of examining plants care- 

 fullv, instead of looking at them superficially. 



The principle upon which the key is constructed is 



