LEAF OF VIBURNUM OPULUS AND V. LANTANA. 245 
In other cases, even in the same genus, this difference occurs. 
Thus in Helianthemum, H. ælandicum and H. canum have no 
stipules, while H. vulgare has. I do not know that any 
explanation has been suggested to account for these differences, 
with which I have attempted to deal in the previous paper 
(ante, p. 217). 
According to DeCandolle’s ‘ Prodromus,’ there are 41 species 
of Viburnum, and though some more must now be added, this 
would not materially affect the question. Of these 41, 35 have 
the leaves entire, and more or less resembling those of V. Lan- 
tana. None of these possess stipules. The other six have lobed 
leaves, more or less like those of V. Opulus, and these all have 
stipuliform appendages, the existence of which would seem, 
therefore, to be connected with the presence of the lobes. 
The existence of honey-glands at the base of the leaf is also, 
perhaps, connected with the texture of the leaf. 
In V. Lantana the covering of felted hairs affords a sufficient 
protection; but the tender young leaves of V. Opulus would 
afford a tempting food to many caterpillars and other insects. 
The ants and wasps which are attracted by the honey would 
tend to keep them down, and thus to serve as a body-guard. 
Indeed, it appears to be the case that on specimens of V. Opulus 
which are much frequented by wasps and ants, the leaves are 
less eaten than in other cases where they are not so protected. 
I now come to the stipuliform appendages. These often bear 
honey-glands, but by no means always, and even where these occur 
there seems no reason why they should be situated on filiform 
appendages. On the whole, then, I doubt whether they can 
be explained as mere honey-glands, or whether, indeed, they are 
of any actual use when the leaves are fully developed. 
When we meet with a small organ which appears to have no 
definite function, we naturally ask ourselves whether it is the 
disappearing relic of some larger organ which at one time 
performed some useful purpose in the economy of the animal or 
plant. This suggestion, however, seems untenable in the present 
case, because, as a matter of fact, we do not find that the stipu- 
liform appendages are more developed in any of the species 
allied to V. Opulus. 
There is, however, a physical cause to which perhaps the 
presence of these organs may be due. We have seen that 
much the larger number of species of Viburnum have entire 
