294 VEGETABLE ORGANOGRAPHY. 



ones, and do not appear so clearly to serve for their 

 envelope : in the former case the name of Scaly Bud 

 is given to the integument formed by the outer leaves, 

 and in the latter we say that the leaves are naked, or 

 vrithout buds. The buds being organs common to the 

 nutritive and reproductive parts, and only being formed 

 by the degeneration of other organs, their detailed study 

 will only be presented to us in the Fourth Book of this 

 work, but we have to examine here the state of leaves 

 from the period of their birth to that of their death ; 

 it must also be remarked, that we will consider their 

 history with regard to their structure, properly so called, 

 and not as regards their physiological functions. 



Leaves, whether considered as enclosed in a bud, or 

 developed naked at their birth, are always, at this age, 

 disposed in such a manner as to occupy the least pos- 

 sible space. Different causes determine their appearance 

 at this period, viz. their position and mode of adherence 

 to the stem, the disposition of their principal nerves, and 

 the different degrees of separation or union of their 

 parts. All the appearances which result from the com- 

 plication of these causes may be reduced to a limited 

 number of folds, or curves, under which all known leaves 

 may be classed. Under this head, leaves are — 1st, 

 folded or rolled lengthways upon the longitudinal nerve, 

 which remains straight; 2d, folded or curved, so that 

 their apex is applied to their base ; 3d, they present 

 sometimes neither curves nor perceptible folds. 



The most usual state of the leaves, or portions of the 

 leaves, of Dicotyledons, and especially of those with 

 petioles which do not sheath, is to be folded lengthways 

 upon their middle nerve, so that the two sides of the 

 limb have a tendency to be applied one upon the other 

 by their upper surface. This appears to be the normal 

 state of all leaves and leaflets with pinnate nerves, but 



