I am tempted to give one more instance showing how plants and animals, remote in the scale of nature, are bound together by a web of complex relations. I shall hereafter have occasion to show that the exotic Lobelia fulgens is never visited in my garden by insects, and consequently, from its peculiar structure, never sets a seed. Nearly all our orchidaceous plants absolutely require the visits of insects to remove their pollen-masses and thus to fertilise them. I find from experiments that humblebees are almost indispensable to the fertilisation of the heartsease ( Viola tricolor ), for other bees do not visit this flower. I have also found that the visits of bees are necessary for the fertilisation of some kinds of clover; for instance twenty heads of Dutch clover ( Trifolium repens ) yielded 2,290 seeds, but twenty other heads, protected from bees, produced not one. Again, 100 heads of red clover ( T. pratense