2*20 LETTER XLIX. 



There are five Classes into which all plants may 

 be divided ; namely — 



I. ExoGENs, or Dicotyledons ; netted-leaved flower- 



ing plants, with two or more cotyledons to their 

 embryo, and seeds enclosed in a seed-vessel. 



II. Gymnosperms ; parallel-veined or fork-veined 



flowering plants, with two or more cotyledons to 

 their leaves, and seeds formed without the pro- 

 tection of a seed-vessel. 



III. Exdogexs, or Monocotyledons ; parallel-veined 

 flowering plants, with only one cotyledon. 



IV. Rhizanths ; leafless parasitical flowering plants, 

 with no cotyledons. 



V. AcROGENS, or AcoTYLEDONs ; plants having no 



true flowers that can be distinguished, and no 

 cotyledons. 



Each class is subdivided according to special rules, 

 and must be treated of separately. 



Class I. EXOGENS. 



The Subclasses are three ; namely — 



1. Polypetalous plants ; in which the petals are all 



distinct. 



2. Monopetalous plants ; in which the petals are 



united into a tube. 



3. Incomplete plants ; in which there are no petals, 



and very often not even a calyx. 



Each of these subclasses may be again subdivided 

 into groups^ as follows : — 



