THE THREE CLASSES. 7 



in a single ring ; the newest formation being internal. 

 A Stem of Corn or Grass, will show this structure. 

 The Stem of a Monocotyledonous Plant, has no dis- 

 tinction of Medullary Rays, or Bark: and from this 

 weaker structure, trees of their Class, live a much 

 shorter period than trees of the first Class : many of 

 which can be found more than 1000 years old ; whilst 

 the most venerable of the second Class can scarcely 

 number 300 years. 



Herbaceous Plants, (those Plants which die down 

 to the ground each year,) of the First Class, are more 

 durable than those of the Second, also ; with a few 

 exceptions perhaps. 



We will now compare the LEAVES : hold up some 

 to the light, and you will see their nerves and veins 

 very distinctly. If the leaves have veins which branch 

 and interlace, like net-work, they belong to Plants of 

 the First Class. But if the leaves have nerves which 

 run parallel to each other, and veins which do not 

 interlace ; we know that they must belong to Plants of 

 the Second Class. PI. I. A 3. B 3. 



There are a very few exceptions to this rule, (the 

 Common Arum, is one,) therefore do not decide to 

 which class a plant belongs, by the veining of the 

 leaves alone ; but observe the growth of the Stem and 



