Let us remark that the peas touch laterally, and are pressed one
against the other, so that the grub, when searching for a point of
attack, cannot circulate at will. Let us also note that the lower pole
expands into the umbilical excrescence, which is less easy of
perforation than those parts protected by the skin alone. It is even
possible that the umbilicum, whose organisation differs from that of the
rest of the pea, contains a peculiar sap that is distasteful to the
little grub.
Such, doubtless, is the reason why the peas exploited by the Bruchus are
still able to germinate. They are damaged, but not dead, because the
invasion was conducted from the free hemisphere, a portion less
vulnerable and more easy of access. Moreover, as the pea in its entirety
is too large for a single grub to consume, the consumption is limited to
the portion preferred by the consumer, and this portion is not the
essential portion of the pea.
With other conditions, with very much smaller or very much larger seeds,
we shall observe very different results. If too small, the germ will
perish, gnawed like the rest by the insufficiently provisioned inmate;
if too large, the abundance of food will permit of several inmates.
Exploited in the absence of the pea, the cultivated vetch and the broad
bean afford us an excellent example; the smaller seed, of which all but
the skin is devoured, is left incapable of germination; but the large
bean, even though it may have held a number of grubs, is still capable
of sprouting.
Knowing that the pod always exhibits a number of eggs greatly in excess
of the enclosed peas, and that each pea is the exclusive property of one
grub, we naturally ask what becomes of the superfluous grubs. Do they
perish outside when the more precocious have one by one taken their
places in their vegetable larder? or do they succumb to the intolerant
teeth of the first occupants? Neither explanation is correct. Let us
relate the facts.
On all old peas--they are at this stage dry--from which the adult
Bruchus has emerged, leaving a large round hole of exit, the
magnifying-glass will show a variable number of fine reddish
punctuations, perforated in the centre. What are these spots, of which I
count five, six, and even more on a single pea? It is impossible to be
mistaken: they are the points of entry of as many grubs. Several grubs
have entered the pea, but of the whole group only one has survived,
fattened, and attained the adult age. And the others? We shall see.
Public-domain text, read in full here on John Shaqi.
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