XII. 



EXOGENS AND ENDOGEXS. 



THE classification of all flowering plants into two 

 grand divisions, called Endogens and Exogens,' 

 although the most natural division in the vegetable 

 kingdom is founded on an error regarding their 

 structure and manner of growth. Exogens may 

 perhaps be properly enough called outside-growers, 

 as the term implies, since the new wood formed 

 each year is produced on the outside of that which 

 existed before, and next within the bark. But 

 endogens can in no peculiar sense be termed inside- 

 growers, since their new growth is likewise formed 

 near the surface of the stem (which in this case is 

 destitute of true bark) and not at the center, as is 

 usually supposed. The difference between the struc- 

 ture of the stems of exogens and endogens are great, 

 but they do not lie in the distinction implied in the 

 names given to the two classes. Exogens, or more 

 properly Dicotyledons (so called because they usu- 

 ally have two first or seed-leaves) produce their wood 

 in wedges which lie side by side with their edge 

 toward the pith of the plant, the different wedges 



» Including Gymnosperms. 



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