Nor is it necessary that the new materials for selection to work upon should be started by hybridisation. Grafting, change of conditions, and even variations so vaguely understood that we term them "spontaneous," may supply the starting-points for changes in the characters of plants, so remarkable after intensification by breeding that people find it difficult to believe they can have come from one stock. Here, however, I must conclude, merely remarking that the above sketch is a mere outline of the subjects modern agriculture and horticulture concern themselves with. There are hundreds of problems connected with the germination of seeds, on which valuable recent work has been done by Klebs, Green, Horace Brown, and others; with the resistance of seeds and seedlings to high and low temperatures, a subject opened out by Sachs, Kny, De Vries, Krasan, Just, Höhnel, Dewar, Dyer, and others; with the conditions of vegetation which affect the various functions of growth, respiration, assimilation, transpiration, and so forth, on which I cannot even touch in these pages. Meanwhile I hope I have succeeded in impressing upon you the grand fact that the plant is a living and very complex engine, driven by the radiant energy of the sun, and capable of doing work thereby, and this just as truly as any heat-engine is driven by chemical energy gained by means of the sun's rays, or as a water-mill is driven by power which must be referred to the energy of potential in the head of water placed in position by the sun's work in evaporation. Fundamentally the whole of life and work on our planet is to be referred to the one great source of energy which renders possible the establishment of differences of potential. This machine, then, doing work in various ways, adapts itself--or goes to the wall--to the conditions of its work among competing organisms or opposing circumstances. Curiously enough, while in some cases it suffers from the competition, in others it is benefited by its life-actions fitting in between those of other organisms, which in their turn supplement it. In other words new types of this engine, capable of doing the work in various ways, are obtainable; some are good types for the conditions afforded, others are bad ones. Examples of both will occur in the further exposition of the subject. Man's position in regard to the struggle is that of an intelligent being who steps in at certain stages and protects, fosters, and in every way favours the agricultural plant--the living machine--and sees that every opportunity is given it to do its best work in the best way--from his points of view! NOTES TO CHAPTER VIII.