The differences between the specimens grown from a single lot of seeds, for instance from the seeds of one self-fertilized capsule are, as I have said, partly due to the divergences which are always present in a bed, even if the utmost care has been taken to make it as uniform as possible. These local differences are ordinarily underrated and overlooked, and it is often considered to be sufficient to cultivate small lots of plants under apparently similar conditions on neighboring beds, to be justified in imputing all the observed deviations of the plants to hereditary inequalities. This of course is true for large lots, whenever the averages only are compared. In smaller experiments the external conditions of the single individuals should always be considered carefully. Lots of one or two square meters suffice for such comparisons, but smaller lots are always subject to chances and [381] possibilities, which should never be left out of consideration. Therefore I will now point out some circumstances, which are ordinarily different on various parts of one and the same bed. In the first place comes the inequality of the seeds themselves. Some of them will germinate earlier and others later. Those that display their cotyledons on a sunny day will be able to begin at once with the production of organic food. Others appear in bad weather, and will thus be retarded in their development. These effects are of a cumulative nature as the young plants must profit by every hour of sunshine, according to the size of the cotyledons. Any inequality between two young seedlings is apt to be increased by this cumulative effect. The same holds good for the soil of the bed. It is simply impossible to mix the manure so equally that all individuals receive the same amount of it from the very beginning. I am in the habit of using manures in a dry and pulverized condition, of giving definite quantities to each square meter, and of taking the utmost care to get equal distribution and mixture with the soil, always being present myself during this most important operation. Nevertheless it is impossible to make the nourishment exactly equal for all the plants of even a small bed. [382] Any inequality from this cause will increase the difference in the size of the young leaves, augment the inequality of their production of organic matter and for this reason go on in an ever increasing rate. Rain and spraying, or on the other hand dryness of the soil, have still greater consequences. The slightest unevenness of the surface will cause some spots to dry rapidly and others to retain moisture during hours and even sometimes during days.