按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
different； for out of 42 leaves drawn into the burrows； no less
than i6 were drawn in by the tips of the needles。 These worms；
however； worked in a careless or slovenly manner； for the leaves
were often drawn in to only a small depth； sometimes they were
merely heaped over the mouths of the burrows； and sometimes none
were drawn in。 I believe that this carelessness may be accounted
for either by the warmth of the air； or by its dampness； as the
pots were covered by glass plates； the worms consequently did not
care about plugging up their holes effectually。 Pots tenanted by
worms and covered with a net which allowed the free entrance of
air； were left out of doors for several nights； and now 72 leaves
were all properly drawn in by their bases。
It might perhaps be inferred from the facts as yet given； that
worms somehow gain a general notion of the shape or structure of
pine…leaves； and perceive that it is necessary for them to seize
the base where the two needles are conjoined。 But the following
cases make this more than doubtful。 The tips of a large number of
needles of P。 austriaca were cemented together with shell…lac
dissolved in alcohol； and were kept for some days； until； as I
believe； all odour or taste had been lost； and they were then
scattered on the ground where no pine…trees grew； near burrows from
which the plugging had been removed。 Such leaves could have been
drawn into the burrows with equal ease by either end； and judging
from analogy and more especially from the case presently to be
given of the petioles of Clematis montana； I expected that the apex
would have been preferred。 But the result was that out of 121
leaves with the tips cemented； which were drawn into burrows； 108
were drawn in by their bases； and only 13 by their tips。 Thinking
that the worms might possibly perceive and dislike the smell or
taste of the shell…lac； though this was very improbable； especially
after the leaves had been left out during several nights； the tips
of the needles of many leaves were tied together with fine thread。
Of leaves thus treated 150 were drawn into burrows123 by the base
and 27 by the tied tips； so that between four land five times as
many were drawn in by the base as by the tip。 It is possible that
the short cut…off ends of the thread with which they were tied； may
have tempted the worms to drag in a larger proportional number by
the tips than when cement was used。 Of the leaves with tied and
cemented tips taken together （271 in number） 85 per cent。 were
drawn in by the base and 15 per cent。 by the tips。 We may
therefore infer that it is not the divergence of the two needles
which leads worms in a state of nature almost invariably to drag
pine…leaves into their burrows by the base。 Nor can it be the
sharpness of the points of the needles which determines them； for；
as we have seen； many leaves with the points cut off were drawn in
by their bases。 We are thus led to conclude； that with pine…leaves
there must be something attractive to worms in the base；
notwithstanding that few ordinary leaves are drawn in by the base
or foot…stalk。
Petioles。We will now turn to the petioles or foot…stalks of
compound leaves； after the leaflets have fallen off。 Those from
Clematis montana； which grew over a verandah； were dragged early in
January in large numbers into the burrows on an adjoining gravel…
walk； lawn； and flower…bed。 These petioles vary from 2。5 to 4。5
inches in length； are rigid and of nearly uniform thickness； except
close to the base where they thicken rather abruptly； being here
about twice as thick as in any other part。 The apex is somewhat
pointed； but soon withers and is then easily broken off。 Of these
petioles； 314 were pulled out of burrows in the above specified
sites； and it was found that 76 per cent。 had been drawn in by
their tips； and 24 per cent by their bases； so that those drawn in
by the tip were a little more than thrice as many as those drawn in
by the base。 Some of those extracted from the well…beaten gravel…
walk were kept separate from the others； and of these （59 in
number） nearly five times as many had been drawn in by the tip as
by the base； whereas of those extracted from the lawn and flower…
bed； where from the soil yielding more easily； less care would be
necessary in plugging up the burrows； the proportion of those drawn
in by the tip （130） to those drawn in by the base （48） was rather
less than three to one。 That these petioles had been dragged into
the burrows for plugging them up； and not for food； was manifest；
as neither end； as far as I could see； had been gnawed。 As several
petioles are used to plug up the same burrow； in one case as many
as 10； and in another case as many as 15； the worms may perhaps at
first draw in a few by the thicker end so as to save labour； but
afterwards a large majority are drawn in by the pointed end； in
order to plug up the hole securely。
The fallen petioles of our native ash…tree were next observed； and
the rule with most objects； viz。； that a large majority are dragged
into the burrows by the more pointed end； had not here been
followed； and this fact much surprised me at first。 These petioles
vary in length from 5 to 8。5 inches； they are thick and fleshy
towards the base； whence they taper gently towards the apex； which
is a little enlarged and truncated where the terminal leaflet had
been originally attached。 Under some ash…trees growing in a grass…
field； 229 petioles were pulled out of worm burrows early in
January； and of these 51。5 per cent。 had been drawn in by the base；
and 48。5 per cent。 by the apex。 This anomaly was however readily
explained as soon as the thick basal part was examined； for in 78
out of 103 petioles； this part had been gnawed by worms； just above
the horse…shoe shaped articulation。 In most cases there could be
no mistake about the gnawing； for ungnawed petioles which were
examined after being exposed to the weather for eight additional
weeks had not become more disintegrated or decayed near the base
than elsewhere。 It is thus evident that the thick basal end of the
petiole is drawn in not solely for the sake of plugging up the
mouths of the burrows； but as food。 Even the narrow truncated tips
of some few petioles had been gnawed； and this was the case in 6
out of 37 which were examined for this purpose。 Worms； after
having drawn in and gnawed the basal end； often push the petioles
out of their burrows； and then drag in fresh ones； either by the
base for food； or by the apex for plugging up the mouth more
effectually。 Thus； out of 37 petioles inserted by their tips； 5
had been previously drawn in by the base； for this part had been
gnawed。 Again； I collected a handful of petioles lying loose on
the ground close to some plugged…up burrows； where the surface was
thickly strewed with other petioles which apparently had never been
touched by worms； and 14 out of 47 （i。e。 nearly one…third）； after
having had their bases gnawed had been pushed out of the burrows
and were now lying on the ground。 From these several facts we may
conclude that worms draw in some petioles of the ash by the base to
serve as food； and others by the tip to plug up the mouths of their
burrows in the most efficient manner。
The petioles of Robinia pseudo…acacia vary from 4 or 5 to nearly 12
inches in length； they are thick close to the base before the
softer parts have rotted off； and taper much towards the upper end。
They are so flexible that I have seen some few doubled up and thus
drawn into the burrows of worms。 Unfortunately these petioles were
not examined until February； by which time the softer parts had
completely rotted off； so that it was impossible to ascertain
whether worms had gnawed the bases； though this is in itself
probable。 Out of 121 petioles extracted from burrows early in
February； 68 were imbedded by the base； and 53 by the apex。 On
February 5 all the petioles which had been drawn into the burrows
beneath a Robinia； were pulled up； and after an interval of eleven
days； 35 petioles had been again dragged in； 19 by the base； and 16
by the apex。 Taking these two lots together； 56 per cent。 were
drawn in by the base； and 44 per cent。 by the apex。 As all the
softer parts had long ago rotted off； we may feel sure； especially
in the latter case； that none had been drawn in as food。 At this
season； therefore； worms drag these petioles into their burrows
indifferently by either end； a slight preference being given to the
base。 This latter fact may be accounted for by the difficulty of
plugging up a burrow with objects so extremely thin as are the
upper ends。 In support of this view； it may be stated that out of
the 16 petioles which had been drawn in by their upper ends； the
more attenuated terminal portion of 7 had been previously broken
off by some accident。
Triangles of paper。Elongated triangles were cut out of moderately
stiff writing…paper； which was rubbed with raw fat on both sides；
so as to prevent their becoming excessively limp when