xl PREFACE. 
ways, it 1s a simple bilobed leaf, or it is an abruptly 
pinnate bifoliate leaf, the leaves cohering by their inner 
margins, or it is a pinnate leaf, reduced to the two 
basal leaftets cohering with the costa of the pinna, this 
last is deserving of little consideration. 
If it is a simple leaf, the midrib of the leaf as it 
exists should be the largest vascular fascicle, and all 
*e other veins should be more or less lateral. 
Yf an abruptly pinnate bifoliate leaf, cohering by the 
ì margin, the midrib will probably be the small- 
‘ne midribs will exist for each lobe, and a macro- 
division or bation may be carried nearly .to ‘the apex 
of the petiole, and this would be analogous strictly, 
- for a mucro always exists,—instance Labiate and Bo- 
I can also cite in reference to the similarity of mo- 
dification between leaves and carpellary leaves, such ins- 
tances as Arum pertusum and Leonitice. 
M. Decandolles’ hypothetical explanation of the de- 
grees of division of leaves appears to me to rest upon 
very inefficient causes, one of which is easily disproved, 
because the degree of lobation ought to correspond 
with the distance between the primary veins. 
