Everyone is familiar with the difference between the ray and central florets of, for instance, the daisy, and this difference is often accompanied with the partial or complete abortion of the reproductive organs.

But in some of these plants the seeds also differ in shape and sculpture.

These differences have sometimes been attributed to the pressure of the involucra on the florets, or to their mutual pressure, and the shape of the seeds in the ray-florets of some Compositae countenances this idea; but with the Umbelliferae it is by no means, as Dr.

Hooker informs me, the species with the densest heads which most frequently differ in their inner and outer flowers.

It might have been thought that the development of the ray-petals, by drawing nourishment from the reproductive organs causes their abortion; but this can hardly be the sole case, for in some Compositae the seeds of the outer and inner florets differ, without any difference in the corolla.