New conditions of life (locality and climate)–unusual food or reproductive activity–act often in a powerful way upon the germ-plasm and cause it to vary–that is to say, they alter some of its qualities, though not necessarily disturbing in any way the general living substance of the organism so far as to produce any important change perceptible to the human eye. In consequence, the young produced after such disturbance of the germ-plasm are found to differ more from their parents than in cases where no such disturbance has been set up by the natural never-ceasing variation of the surrounding world. This fact is well known to horticulturists and breeders, and is made use of by them. When a gardener wishes to obtain variations of a plant from which to select and establish a new breed, he deliberately sets to work to disturb–to shake up, to act upon in a tentative, experimental way–the germ-plasm of one or more parent plants by change of soil, climate, food and often by cross-fertilizing them with another breed or variety. In this way he to some extent "breaks" the constitutional stability of the germ-plasm of the plant and obtains abundant "variations" in the offspring. These are not precisely foreseen, and show themselves in all parts of the new generation. But some of them are what the gardener wants, and are "selected" by him for retention, rearing and breeding. The response of the germ-plasm of organisms to the stimulus of new environmental conditions has been compared to that of the well-known pattern-producing toy–the kaleidoscope. The bits of glass, beads and silk which you see in a kaleidoscope, forming by reflection in its mirrors a beautiful and definite pattern, are changed by a simple vibration caused by tapping the instrument into a very different pattern, the coloured fragments being displaced and rearranged. The apparent change or variation is very great though produced by slight mechanical disturbance, and the new pattern is altogether without any special significance–the fortuitous outcome of a small displacement of the constituent coloured fragments. We can imagine that similarly slight disturbances of the organic molecules of the germ-plasm may produce considerable and important variations in it and the new growth to which it gives rise: and, further, that these variations may prove to be either (1) injurious, or (2) of life-saving value, or often enough (3) of no consequence whatever although bulking largely in our human eyes and thereby misleading our judgment of them.