336 REV. GEORGE HENSLOW ON THE 
when insects of any particular species first punctured oaks. It is well known that in q | 
the human subject there may be a predisposition for tumourous or cancerous growths ` 
which is hereditary ; and there would seem to be a very close resemblance between 1 | 
tumours and galls, both being hypertrophied conditions of certain normal tissues. For ~ 
example, Sir B. C. Brodie thus describes a fatty tumour :—“ There is no distinct boun- - | 
dary to it, and you cannot say where the natural adipose structure ends and the morbid 1 
growth begins." Such is very much like the growth of galls, which is due to cell-division 1 | 
setting in at certain points of the epidermis and subjacent tissues. But although lesions 1 | 
and mutilations will not, as a rule, prove to have any hereditary effects, yet the constant 1 | 
drain upon a secreting organ may. A mutilation being once made, the place heals, and | 
there is an end of all vital action; but if a constant drain be kept up upon an organ 1 | 
thus irritated, and made to secrete, there will be a corresponding flow of nutriment to 1 
the place, which must also affect more or less the adjacent parts. j 
Mr. Darwin, in speaking of the Cow, observes :—‘‘ We may attribute the excellence 4 
of our cows, and of certain goats, partly to the continued selection of the best milking 4 
animals, and partly £o the inherited effects of the increased action, through man’s art, of — 
the secreting glands” (Anim. & Pl. under Domest. ii. p. 300). 1 
This fact, recorded in the last sentence, which I have italicized, I take as the basis of 3 
my hypothesis :—That insects again and again visiting the same flowers will thus cause a 1 
constantly repeated flow of nutrition, which affects (I assume) not only the glands them- 4 
selves, which thus become hypertrophied, but the adjacent parts, such as the corolla and ` 
stamens ; and there would be an à priori probability of vegetable structures being thus ` 
more likely to be affected than animal, because there is no well-defined or bounded ` 
channel to conduct the sap solely to the one point of irritation. Such, then, I would d 
advance, hypothetically, as a vera causa for the origin of all conspicuous flowers. E 
Natural selection might come into play and determine the final result. E 
We might, perhaps, go a step further, and speculate as to the origin of irregularity 13 
in flowers, by regarding them, so to say, as having a kind of plasticity which will enable ` 
them to respond to repeated irritation, in some sort of way analogous to that of tendrils of ` 
the Virginian Creeper, which also respond to mechanical irritation, then develope secreting 
organs and become hypertrophied. So that as long as insects visit a flower they are 
continually keeping up a sort of irritation at that region, the whole weight of the insect 
being often thrown upon the corolla. If it be terminal, the insect alights on any petal 
or petals, and nothing induces the flower to become irregular* ; but if the flower be axil- 
lary, it alights on the anterior side, and so (I assume theoretically until it can be demon- 
strated or disproved) brings a stimulus which is responded to by the inherent forces of 
the plant, and which causes the flower to become bilateral, by determining a super 
abundant flow of nutriment to that part. What it is that determines the peculiarities 
of structure in each flower respectively, causing irregular flowers to be so very different, ` 
it is quite impossible to say. This constant irritation and the continual drain iu the | 
secretive organs must stimulate them to develope more and more, just as à man’s arm | 
... * Of course I do not mean Ge any single flower is thus affected, but that the ros is "€ acquired after 
many generations. 
