jourilS MaSTKoe!] ^oyd MicTosGojpical Society. 1 6 1 
be inferred to be hi-fid, but rather duplex. They are in reahty 
double leaves, and it is on this hypothesis alone that their true 
structure can, I humbly submit, be interpreted. 
If now we examine one of these double leaves, we find it pre- 
senting a normal and an abnormal venation — the one that of the 
separate leaflets on the rest of the leaf, the other that resulting 
from their junction. The normal venation shows itself on the 
outside of each rib, where it could not have sufiered change from 
anastomosis ; it peeps out also in the lobes, which are in reality the 
free projections of the several leaflets. But the course of the veins 
becomes disturbed and irregular in that region of the double leaf 
where the two leaflets appear to coalesce into one; this may be 
illustrated by a rough diagram (A, Plate V.), in which the double 
leaf, or, what I suppose to be synonymous, the bilobed simple leaf, 
is seen to consist of : — 
EXPLANATION OF THE DIAGRAM, A, PLATE Y. 
1. — LC 'L, Intercostal space, bounded by the costjB (ribs), CL, C X. 
2. — LAS, Lobular space, in which the vessels of the primitive leaflets are 
unaltered by anastomosis, 
3. — 0 H L, Portion of leaf outside each costa, in which the veins are unaltered 
by anastomosis. 
4. — OS, Commissural region, wliere the veins and veinlets from the two adja- 
cent leaflets anastomose. 
5. — Interlobular space, the depth of which is regulated by the breadth of the 
typical leaflets, and by tiie angular divergeuce of the costse, L C 'L, 
6. — L X, Apices of the lobes. 
7. — S, Sinus between the lobes, where the coalescence between the two primi- 
tive leaflets ceases. 
8. — L S, X S, Edges of primitive leaflets, which retain their original outline, 
marginal divisions, teeth, segments, &c., unaltered by coalescence.* 
All this is in strict conformity with what can be demonstrated 
as true of the structure of the lobed leaf, and the foregoing example 
may be cited as an instance of the fewest elements of which it is 
possible for a lobed leaf to consist. For a lobed leaf must have at 
least two lobes ; and if two lobes, two ribs ; and if two ribs, two 
particular sets of veins ; t and if two sets of veins, one similar to 
the other ; and if both alike and joined into one, this is a double 
leaf, and, as I conceive, the simplest form of the lobed one. These 
features, one and all, are clearly discerned in the metamorphosis of 
the Bramble leaf, and will be found verified and repeated in any 
ordinary lobed leaf we may choose to examine for the purpose. 
The relation between the compound and the lobed leaf is thus 
established. 
* It is not to be understood that the leaflets overlap, or that the veins intersect ; 
tlie diagram being designed merely for the purpose of defining the regions in 
which the veins become altered or remain unaltered by anastomosis. 
t " In lobed leaves, which may be considered as simple leaves approaching 
composition, each rib has its own particular set of veins." — Lindley, ' Introd. 
Bot.' 
