Cross Fertilisation

Abstract

THERE could perhaps be found no more striking illustration of the law which seems to demand, from all species of living things, frequent crossing as a condition of their continued existence, than is afforded in the structure and development of the flowers of Lobelia. A hasty examination of a few specimens of this plant might seem to refute this idea; and I can imagine an anti-Darwinian, unacquainted with the life-history of the flower, pointing triumphantly to it, not only as an instance of pepetual self-fertilisation, but also as an incontrovertible example of an organism specially adapted to the use and convenience of a different species, without itself deriving any advantage from the circumstance. For while the flowers of this genus are furnished with a broad and brilliantly-coloured lip, forming an attractive lure on which insects may alight to feed on the nectar provided for them, the introrse anthers are connected together, so as to form a rigid case completely enclosing the style and imbedding its summit in pollen. In this case, then, insect agency appears to be worse than useless; for though a few grains of pollen may be, and are, shaken out, through a small orifice between the extremities of the anthers, upon the back of every moderate-sized insect which enters the flower; such grains can apparently never be brought into contact with the stigma, and consequently must perish and be wasted. How completely, however, would such a reasoner find the tables turned by more continued observation. Lobelia is one of those genera which might be more correctly described as versisexual than, as strictly speaking, hermaphrodite. Its flowers are at first entirely male, die female organs not being fully developed till after all the pollen has been removed. Then the style forces its way between the extremities of the anthers, and expands into a broad stigma, so situated as to rub the backs of the bees and other insects that enter the flower, and brush off any pollen that they may bring. Thus, self-fertilisation, instead of being, as it at first seemed, inevitable, is in fact impossible; and insect agency, which appeared at best useless, is absolutely necessary to the survival of the species.