Increased intensity of colour often accompanies teratological changes; an instance has just been alluded to in the _Gesnera_; the feather hyacinth, _Muscari comosum_, furnishes another illustration, the adventitious pedicels being brightly coloured. In fasciated stems, also, of herbaceous plants, it not unfrequently happens that the upper portions of the stem are brightly coloured. The occurrence of flowers or fruits of different colours on the same plant, or even in the same cluster, is a phenomenon which does not come within the scope of the present book; the reader may, however, be referred to the excellent summary on this subject published by Mr. Darwin in his work on the 'Variation of Animals and Plants under Domestication.' FOOTNOTES: [372] These deviations are treated of under the head of alterations of form, because they are not, in a teratological point of view, of sufficient importance to demand a specific heading, while they appeal to the sight in the same way as the deviations from the customary forms of organs. [373] 'De Antholys,' p. 32, Sec. 38. [374] 'Bull. Acad. Belg.,' xvii, part 2, p. 131, c. tab. [375] See Cramer, 'Bildungsabweich,' pp. 17, 55, 82, 65. See also Lucas, 'Verhandl. des Bot. Vereins. Brandenb.,' heft 1, 2, _Anchusa_. Christ, 'Flora,' 1867. pp. 376, tab. 5, 6, _Stachys_. BOOK III. DEVIATIONS FROM THE ORDINARY NUMBER OF ORGANS. To a certain extent the number of the organs of a plant is of even greater consequence for purposes of classification than either their form or their arrangement; for instance, the number of cotyledons in the embryo is made the chief basis of separation between the two great groups of flowering plants, the monocotyledons and the dicotyledons. In the one group, moreover, the parts of the flower are arranged in groups or whorls of five; in the other the arrangement is ternary. In mosses the teeth of the peristome are arranged in fours, or in some multiple of that number. So far as the larger groups are concerned, and also in cases where the actual number of parts is small, the numerical relations above described are very constant; on the other hand, in the minor subdivisions, and especially where the absolute number of parts is large, considerable variation may occur, so that descriptive botanists frequently make use of the term indefinite, and apply it to cases where the number of parts is large and variable, or, at any rate, not easy to be estimated.