WHY THE LEAVES FALL. 
373 
the leaf-scar is circular, in other words, where the leaf-stalk is 
cylindrical, and the bundles of woody tissue are arranged in 
a ring, the leaf would be less easily detached than in cases 
where the bundles form a half-circle, merely leaving the upper 
surface of the leaf-stalk comparatively weak from the presence 
of cellular tissue only. In any case, the leverage exerted by 
the flat surface of the leaf, acted on by every wind that blows, 
must be taken into account. 
Another reason that has been suggested for the removal of 
the leaves, is the pressure exerted on the base of the leaf-stalk 
by the axillary buds, which swell and increase in size notably in 
the autumn ; but there are many things which show that the 
swelling of the bud at this time of year has but little to do with 
the shedding of the foliage ; for see how carefully pressure is 
provided against by the flattening of the leaf-stalk at its base, or 
even by its being scooped out spoon fashion to receive the bud. 
Again, notice how often, when there is a chance of injurious 
pressure being exerted, the stem bends away from the leaf 
at an angle, as in what are called “ flexuose ” stems, so that no 
hurtful pressure can take place. For the purpose of testing this 
notion, we have, while writing these notes, observed a young 
lime, which even thus early (August 7) is shedding its leaves. 
The lime is a good tree to notice for this purpose, because its 
stems are often more or less flexuose, and because its leaf-buds 
are placed a little on one side of the leaf-stalk, and not im- 
mediately in their axil ; moreover, as happens of course with 
other trees, only a small proportion of the leaves foster in their 
axils buds large enough to exert any possible pressure. The 
vast majority of the axillary buds remain u latent.” 
Now it might be expected, if it were true that the newly 
formed buds pushed off the old leaves in autumn, that the lime- 
tree would retain its leaves longer than most other trees, seeing 
that its buds are not so placed as to be able to exert much 
pressure, and that the stem is more or less flexuose. But what 
is the case ? The lime is one of the earliest trees to part with 
its leaves, and as the writer has observed, not only in the lime, 
but in other trees, the presence or absence of an axillary bud 
does not seem to make the slightest perceptible difference, 
either in the period at which the leaves fall, or in the amount 
of force requisite to detach them artificially. For experiments 
of this kind, the common and the Neapolitan alder are suitable, 
inasmuch as some of the buds in these trees are raised upon 
short stalks, which, growing comparatively fast just before the 
fall of the leaf, might be supposed to exert some influence on 
that phenomenon. But here, again, the comparison of those 
leaves which are provided with stalked buds, and those in which 
no bud or only a rudimentary one is visible, does not show any 
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