conclude from the fact that the bees are _not absolutely constant_ that flowers are not fertilized by bees at all? I cannot conclude this note without touching briefly upon what the opponents of the flower theory have contributed, and what explanation of the facts they are prepared to offer. In his important work, _Mechanische-physiologische Theorie der Abstammungslehre_, published in 1884, Nägeli, as a convinced opponent of the theory of selection, attempted an explanation. He was quite aware that his assumption of an inward 'perfecting principle' would not suffice to explain the mutual adaptations of flowers and insects, and he refers the transformation of the first inconspicuous blossoms into flowers to the mechanical stimulus which the visiting insects exerted upon the parts of the blossom. By the pressure of their footsteps, the pushing and probing with their proboscis, they have, he says, transformed gradually, for instance, the little covering leaves at the base of a pollen vessel into large flower petals, caused the conversion of short flower-tubes into long ones, and of the pollen, once dry and dusty, into the firmly adhesive mass formed in the anther lobes of our modern flowers. The colour of the flowers depends, according to him, upon the influence of light, which certainly no more explains the yellow ring on a blue ground in the forget-me-not than it does the many other nectar-guides which show the insect the way to the honey. Nägeli works with the Lamarckian principle in the most daring way, and with the same _naïveté_ as Lamarck himself in his time, that is, without offering any sort of explanation as to how the minute impression made, say by the foot or by the proboscis of an insect, upon a flower, is to be handed on to the flowers of succeeding generations. He treats the unending chain of generations as if it were a single individual, and operates with his 'secular' stimulus, and with 'weak stimuli, lasting through countless generations,' as though they were a proved fact. But I have not even touched upon the question as to whether these 'stimuli' could produce the changes he ascribes to them, even if they were continually affecting the flower. How the scale-like covering leaves of the pollen vessels could become larger and petal-like through the treading of an insect's foot is as difficult to see as why a honey-tube should _become longer_ because of the butterfly's honey-sucking: might it not just as well become _wider_, _narrower_, or even _shorter_? I see no convincing reason why it should become _longer_! And even if it did so, it would necessarily continue to lengthen as time went on, and this is not the case, for we find corolla-tubes of all possible lengths, but, _it is to be noted, always in harmony with the length of the proboscis of the visiting insect_. In a similar way Henslow has recently attempted to refer the origin of flowers to the mechanical stimulus exercised upon it by the visiting insects.