OF PLANTS. 
197 
But (to pursue this great work in its progress) the im¬ 
pregnation, to which all this machinery relates, being com¬ 
pleted, the other parts of the flower fade and drop off, whilst 
the gravid seed-vessel, on the contrary, proceeds to increase 
its bulk, always to a great, and in some species (in the 
gourd, for example, and melon,) to a surprising compara¬ 
tive size; assuming in different plants an incalculable va¬ 
riety of forms, but all evidently conducing to the security 
of the seed. By virtue of this process, so necessary but 
so diversified, we have the seed at length, in stone-fruits 
numerous species of these lively little beings may be seen in almost 
every expanded flower; and whether they are in search of honey, which 
is contained in the nectaries of many flowers, or whatever may be the 
object of their attraction, by being continually on the move, they, no 
doubt, further the dispersion of the pollen, and thus, in a great measure, 
contribute to the fertility of the plants they visit. 
In many plants, as those which belong to the Linnaean class dicecia, 
where the stamens and pistils are in separate flowers, and those flowers 
situated on two separate plants of the same species, the operation of 
insects, or the efficacy of winds, is indispensably necessary to the per¬ 
fecting the fruit, by transporting the pollen of the one to the stigma of 
the other. 
Some plants, indeed, that have perfect, or united flowers, have the 
anthers so situated that it is almost impossible the pollen can, of itself, 
reach the stigma; in this case insects generally become the auxiliaries 
to the fertilization of the seed. An instance of this may be seen in the 
aristolochia clematitis. “According to Professor Willdenow, the flow¬ 
er of this plant is so formed, that the anthers of themselves cannot im¬ 
pregnate the stigma; but this important affair is devolved upon a par¬ 
ticular species of tipula, (T. pennicornis. ) The throat of the flower 
is lined with dense hair, pointing downward so as to form a kind of fun¬ 
nel, or entrance like that of some kinds of mouse-traps, through which 
the insects may easily enter but not return: several creep in, and, un¬ 
easy at their confinement, are constantly moving to and fro, and so de¬ 
posit the pollen upon the stigma: but when the work intrusted to them is 
completed, and impregnation has taken place, the hair which prevented 
their escape shrinks, and adheres closely to the sides of the flower, and 
these little go-betweens of Flora at length leave their prison. A writer, 
however, in the Annual Medical Review (ii. 400,) doubts the accuracy of 
this fact, on the ground that he could never find T. pennicornis, though 
A. clematitis has produced fruit two years at Brompton.” Introduc¬ 
tion to Entomology, by Kirby and Spence , vol. i. p. 298. 
That the tipula pennicornis does enter the flowers of aristolochia 
clematitis, as recorded by Professor Willdenow, I can confidently af¬ 
firm, from having observed them in great plenty in the inflated base of 
the corolla every year, for these last fifteen years, in the Oxford Botanic 
Garden, where the plant generally forms fruit. The first time I found 
this insect in the flowers of the above species of aristolochia, was on 
the 12th of July, 1812, at Godstow, near Oxford, where the plant was 
then growing in a wild state near the ruins of the nunnery. 
For the above observations the editor is indebted to an exellent bot¬ 
anist, Mr. W. Baxter.— Paxton. 
