that this degeneration is due to lack of nutrition, by removing the inferior flowers from a young bunch, but we are unaware that the experiment has been made. In Viburnum tomentosum (fig. 82) the flowers are arranged in a compound corymb and occur in two forms. The central flowers have a small corolla, five stamens, and a well-developed pistil B FIG. 82-Flowers from the same inflorescence of Viburnum tomentosum. A, sterile flower with rudimentary pistil and no stamens.-B, sterile flower with very rudimentary pistil and stamens.-C, flower with two fertile stamens; the other three stamens and the pistil are rudimentary.-D, fertile hermaphrodite flower. (fig. 82, D). The eight or nine peripheral flowers of each inflorescence have the corolla much larger, but the stamens are absent and the pistil is rudimentary (fig. 82, A). The petals turned towards the outer side are much the largest, and it is not rare for the petals turned towards the inner side to be hardly larger than those of the central flowers. What is important to notice, as it bears out the relation between degeneration and lack of nourish ment, is that a smaller petal is always associated with a larger stamen (fig. 82, B, C). In Viburnum opulus, the wild guelder-rose, there are also two kinds of flowers, the central flowers which are sexual and hermaphrodite, and the peripheral flowers which are sterile and possess a very large corolla. The five petals are, however, equal in size, and there are no forms transitional between the sterile and sexual flowers. The cultivated guelder-rose is a variety of the wild form in which all the flowers are sterile and possess a large corolla: the plant has completely lost the power of sexual reproduction. § 4. Atrophy without apparent cause. In many cases it is impossible to determine the cause of atrophy. Why, for instance, has half the inflorescence disappeared from a unilateral cyme ? Why have some composites like Artemisia or Rosacea like Poterium lost their habit of being fertilized by the agency of insects, and become anemophilous without conspicuous perianth? Nor can we explain why many Myriapods are blind, although they live in association with species possessing eyes and in conditions where vision apparently would be useful. Semper discovered, in brackish water in the Philippines, Crustacea (Cymothoë) which were completely blind, although they lived in light. The cause of such atrophies is unknown. Moreover, we know that organs may atrophy through correlation with other degenerating organs, or because the whole organism is degenerating although there are no obvious anatomical bonds present between the related parts. As instances of such atrophies we may mention degeneration of the brain resulting on degeneration of the supra-renal capsules; or of the condition of myxodoma resulting from mechanical or functional disturbance of the thyroid gland. When the essential sexual organs of the male or female are congenitally or accidentally absent, the secondary sexual characters -the beard, voice, hair, and whole male or female aspect of the body degenerate. When one eye becomes injured or diseased, a frequent consequence is sympathetic degeneration of the undamaged eye. To these cases of correlative atrophy we may add the cases of leaves on many plants with drooping or horizontal branches. On these, the leaves on the upper aspect are frequently rudimentary. The appearance is most striking where the leaves are opposite the pairs being at right angles to one another. In a branch of Acer campestre which is upright, all the leaves are of the same size. In a drooping branch the leaves turned towards the sky are small. In plants belonging to very different families (Acanthaceæ, Melastomaceæ Urticaceæ, etc.) oblique branches exist, and the failure in development of the dorsal upper leaves is invariable. In Procris laevigata (fig. 83) the reduc tion of these leaves has gone very far, but in Klugia notoniana the leaves in the corresponding FIG. 83.-Branch of Procris laevigata. F'f', F"f", F"f". The successive pairs of leaves in the axil of a large leaf F' is a female inflorescence; in the axil of a small leaf f" is a male inflorescence. (The original drawing was made at Buitenzorg in Java by Mas Kromohardjo, a Malay draughtsman.) position are absent. In another representative of the same family (Streptocarpus monophylleia), the degeneration has gone still further; all the leaves are absent and a single greatly enlarged cotyledon is the sole assimilating organ.1 It is evident that in these oblique and horizontal branches, the leaves directed vertically towards the sky are in the most unfavourable position for assimilation, and that, in addition, their presence would shade the leaves lying under them. In these species the more or less complete reduction is an inherited fixation of a sacrifice of these particular leaves for the benefit of the whole organism. CHAPTER II ATROPHY OF INSTITUTIONS THE causes of atrophy in institutions are more or less analogous to those which bring about atrophy of organs. First, there is atrophy from want of use, when function either becomes useless or is transferred to another institution. Atrophy from lack of resources corresponds precisely with atrophy from lack of nutrition. There is nothing, however, in the atrophy of institutions quite analogous to that which, in organisms, results from lack of space. But if the development of an institution cannot be actually impeded by the co 1 See the figures of plants of this family in Fritsch, Gesneriaceœ. (Engler und Prantl's natürlichen Pflanzenfamilien. Leipzig, 1891.) |