LETTER XVm. 



DISTINCTIONS OF EXOGENOUS OR DICOTYLEDONOUS, 

 AND OF ENDOGENOUS OR MONOCOTYLEDONOUS 



PLANTS THE NARCISSUS TRIBE THE CORNFLAG 



TRIBE. 



(Plate XVIII.) 



In my last letter I took leave of Dicotyledonous 

 plants, whieh I am persuaded you are by this time 

 able to recognize by their general aspect, as well as 

 by the technical distinctions to which I have chiefly 

 called your attention. It is not their netted leaves, 

 nor the concentric circles in their stems when woody, 

 nor the two-seeded lobes of the embryo alone, by 

 which they are known, but also other characters 

 in combination with those. Their leaves are usually 

 jointed with the stem, so that they are thrown off at 

 certain seasons : in deciduous trees in the autumn, 

 in evergreens in the spring or summer ; their flowers, 

 if perfect, or nearly so, are mostly divided by four or 

 five ; that is, have four or five sepals, and four or five 

 petals, either distinct or combined ; and finally, their 

 mode of growth is, in general, by branching re- 

 peatedly to form round-headed trees, or broad 

 spreading bushy herbs. All these circumstances are 

 characteristic of Dicotyledonous plants ; but most of 

 them are occasionally subject to exceptions. When 

 exceptions occur in regard to any one circumstance, 



