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LINNEAX SOCIETY OF LONDON. 127
space, these leaves are folded more or less like a fan, iii tlie same
manner as those of Maples, Sycamores, Planes, &c., and this gives
them their lobed form. As regards the stipuliform appendages, the
genus contains some fifty species, of which about forty have oval
leaves without appendages, while the remainder have lobed leaves
with appendages. The presence of these appendages seems, therefore,
to go with that of the lobes. I believe that they assume that
pecuhar thread-like form so as to fill up a space which would otherwise
be left empty in the bud. Maples have no stipules, but in them
the younger leaves in the bud just fill up the interspaces left between
the older ones. In the lobed-leaved Guelder Eoses this is not the
case, but a space remains, which is just occupied by the stipuliform
appendages.
(4.) " On the Presence and Functions of Stipules." Vaucher,
in his ' Histoire Physiologique des Plantes,' speaking of Heliantheinum,
says:— " J'indique dans ce genre deux principaux
objets de recherche. Le premier est la raison pour laquelle
certaines especes ont des stipules, tandis que d'autres en sont
privees." No one, however, so far as I know, has yet attempted
to answer this question, which, however, is one of considerable
interest, and might be asked with reference to several other groups
besides the genus Helianthemum. In attempting to answer this
question, we may begin by considering the function or functions
which stipules perform. Of these, the primary purpose is to protect
the bud. In others they seiTC as accessory, or deputy, leaves.
As an illustration of the former may be mentioned some species of
Viola; of the latter, certain species of Lathyrus—for instance,
L. Nissolia. The question may further be asked. What is the
advantage to the plant in having the purpose of the leaves fulfilled
by stipules instead of true leaves ? Now, L. Nissolia is a species
which lives among grass. Here, then, the same considerations
which render it an advantage to grasses to have long leaves affect
equally the Lathyrus. Again, if, when so growing, the leaves of L.
Nissolia had resembled those of most other Lathyrus, they would,
perhaps, have been dangerously conspicuous. The similarity of the
stipules to the leaves of grasses by which they are surrounded
perhaps enables them to escape observation, and to avoid being
eaten. It may, indeed, be asked why the leaflets should not have
assumed the long linear outline. But, even so, if they had been
arranged at right angles to the petiole, the plant would have been
much less grass-like, and consequently much more conspicuous
than is now the case. This may, I think, be the reason which has
led to the replacement of leaves by stipules in this species, and to
the peculiar form which the latter have assumed. Passing on now
to the cases in which the stipules serve to protect the young loaves,
I may first mention in passing those instances in which the stipules
with this object have become stiff, pointed, or thorn-like, as in
llubinia. In far more numerous species, however, the stipules
protect by enveloping the young bud and leaves. In such groups
the view that the function of the stipules is mainly to protect the
young leaf is confirmed, not to say proved, by the fact that they are