With respect to the crossing of individuals belonging to the same sub-variety, Gaertner, whose accuracy and experience exceeded that of all other hybridisers, states[284] that he has many times observed good effects from this step, especially with exotic genera, of which the fertility is somewhat impaired, such as Passiflora, Lobelia, and Fuchsia. Herbert also says,[285] "I am inclined to think that I have derived advantage from impregnating the flower from which I wished to obtain seed with pollen from another individual of the same variety, or at least from another flower, rather than with its own." Again, Professor Lecoq asserts that he has ascertained that crossed offspring are more vigorous and robust than their parents.[286] General statements of this kind, however, can seldom be fully trusted; consequently I have begun a series of experiments, which, if they continue to give the same results as hitherto, will for ever settle the question of the good effects of crossing two distinct plants of the same variety, and of the evil effects of self-fertilisation. A clear light will thus also be thrown on the fact that flowers are invariably constructed so as to permit, or favour, or necessitate the union of two individuals. We shall clearly understand why monoecious and dioecious,--why dimorphic and trimorphic plants exist, and many other such cases. The plan which I have followed in my experiments is to grow plants in the same pot, or in pots of the same size, or close together in the open ground; to carefully exclude insects; and then to fertilise some of the flowers with pollen from the same flower, and others on the same plant with pollen from a distinct but adjoining plant. In many, but not all, of these experiments, the crossed plants yielded much more seed than the self-fertilised plants; and I have never seen the {128} reversed case. The self-fertilised and crossed seeds thus obtained were allowed to germinate in the same glass vessel on damp sand; and as the seeds successively germinated, they were planted in pairs on opposite sides of the same pot, with a superficial partition between them, and were placed so as to be equally exposed to the light. In other cases the self-fertilised and crossed seeds were simply sown on opposite sides of the same small pot. I have, in short, followed different plans, but in every case have taken all the precautions which I could think of, so that the two lots should be equally favoured. Now, I have carefully observed the growth of plants raised from crossed and self-fertilised seed, from their germination to maturity, in species of the following genera, namely, Brassica, Lathyrus, Lupinus, Lobelia, Lactuca, Dianthus, Myosotis, Petunia, Linaria, Calceolaria, Mimulus, and Ipomoea, and the difference in their powers of growth, and of