THE LEAF. 25 



green colour, and somewhat smooth j that the under surface is of a 

 lighter hue, and divided into two parts by a central or mid rib, (F.40, 

 b b,) from which are sent out several lateral nerves: that the mid rib 

 is nothing more than a continuation of the foot-stalk (a) or the part 

 by which it is connected to the branch ; that the tase (c c) expands 

 on each side of the foot-stalk and proceeds to form the margin (e e) 

 or the boundary of the disk (by which term is meant, the intermedi- 

 ate substance of the leaf,) and that the leaf finally terminates with an 

 a^xor point (d). 



5. That all these parts are present in every expanded 

 leaf, we have many instances to convince us of the con- 

 trary ; for although they are to be met with in numerous 

 vegetables, still there are several plants whose leaves 

 have not so many distinguishing marks. 



All leaves which are sessile have no foot-stalk, and many neither a 

 midrib or lateral nerves, since the nerves sometimes run in a paral- 

 lel direction one with another, as in the leaves of the hyacinth, and 

 several others of that tribe. Again, in many other plants, the leaves 

 being round, or roundish, they have no terminating point ; it is there- 

 fore very clear, that all the parts we have mentioned are not com- 

 mon to every expanded leaf. 



