294 DEVELOPMENT OF LEAVES. [BOOK i. 



immediately below the base of the leaf, the other is directly 

 opposite this base. These rims afterwards become semi- 

 circular, convexo-concave valves, enveloping the axis and 

 touching each other at their edges ; they then form the organs 

 considered as stipules; but they are never in organic con- 

 nection either with the leaflets, or with the petiole, which is 

 contrary to what is generally observed in stipules of compound 

 leaves. 



" Conclusion. The way in which I am led from the above 

 facts to regard the formation of leaves is shortly as follows : 



All leaves are produced on an axis, and their first form is 

 that of a tumour. The lobes, segments, or leaflets on the 

 lower half of a completely formed leaf, are produced from the 

 axis, after the lobes, segments, or leaflets on the upper half. 



The original tumour corresponds with the apex of the leaf, 

 or with the summit of the common petiole. 



In all leaves, the blade and top of the petiole are formed 

 before the stipules and the lower part of the petiole. 



The formation of compound leaves consists of two stages ; 

 first, that of a simple leaf; then that of a pinnate leaf. It is 

 not very probable that the second owes its origin to the axis 

 of the leaf bud as the first does. 



The petiole (either of a simple or of a compound leaf) 

 ought, whether we regard its position relative to the axis or 

 its anatomical structure, to be considered as an immediate 

 elongation of the axis ; it certainly has a great influence on 

 the formation of the leaf. 



The stipel is formed after the point of the leaflet which it 

 accompanies ; its development is generally much slower than 

 that of a stipule. 



All the parts of a leaf are symmetrical from their birth, 

 and the rudiment of each leaf is a body symmetrical in its 

 relation to the axis. 



The young leaflets of all compound leaves, are always 

 opposite. 



All the parts of a rudimentary leaf are capable of develop- 

 ment. This development generally proceeds from the apex 

 to the base of the leaf, and is greater and stronger towards 



