If one compares _any two plants_ of the same kind ever so closely, it will be found that they _differ from each other_. The difference is apparent in size, form, colour, mode of branching, number of leaves, number of flowers, vigour, season of maturity, and the like; or, in other words, all plants and animals _vary from an assumed or standard type_. If one compares _any two branches or twigs_ on a tree, it will be found that they differ in size, age, form, vigour, and in other ways (Fig. 1).…
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