tiiS VEGETABLE ORGANOGRAPHY. 



with phyllodia. We shall shortly see that this term of 

 leaf is likewise often confounded with those of leaflet or 

 segment. 



Section III. 



Of the Disposition of the Nerves in the Limb of the Leaf. 



If the distinction which I have endeavoured to esta- 

 blish between the petiole and limb of leaves has been 

 attentively followed, it will be seen that these two 

 organs differ essentially in two respects. 1st. Petioles, 

 whatever be their form or nature, are composed of 

 parallel fibres ; and if the parallelism is not exact, the 

 fibres are generally more distant at the base, and nearer 

 together above. .2d. Limbs present all the fibres or 

 nerves diverging more or less at the base, whatever may 

 be their ulterior direction : it is this mode of divergence 

 of the fibres of the limb that we liave now to examine. 



I/et us commence first by excluding from this exami- 

 nation a certain number of leaves, the nerves of which 

 are so weak, so indistinct, or so completely buried in the 

 cellular tissue, that their direction cannot be known with 

 certainty : these are the leaves of fleshy or succulent 

 plants, as those of the Ficoids, or the bases of petioles 

 reduced to the state of membranous scales, as the scales 

 which represent the leaves of Asparagus and Ruscus. 

 The principles which I am about to set forth may doubt- 

 lessly be applied to them, but witli such modifications 

 and difficulties as would he injurious to the understand- 

 ing of the general laws. 



The fibres which were united together in the petiole, 

 and proceeded there nearly parallel to each othex-, diverge, 



