the function of the calyx has been reduced, or has disappeared on account of the transference of its function.

(6) Atrophy of roots.—Roots in most plants perform two functions: they fix the plant in the soil, and, chiefly by means of the delicate hairs on their youngest parts, they absorb water and dissolved mineral substances. Sometimes, however, instead of having root-hairs, the rootlets enter into a kind of partnership with a fungus, which lives in their tissues, and absorbs by its processes the necessary food materials from the soil. The pine and beech are examples of this.

In some orchids (Corallorhyza, Myrmechis) the fungi lodge in the subterranean part of the plant, and the branches, having no function, disappear.

In most of the epiphytic Bromeliaceæ the roots are useful only to anchor the plants; the absorption of water takes place entirely through new organs developed from the leaves. The roots are few in number and small, and after the plant has obtained a firm position their growth almost ceases. In another species (Tillandsia usneoïdes) of the same family the roots have completely disappeared.1 This plant, called by the Brazilians, "the plant of the air," fixes itself to branches of trees by its leaves, and is easily transported by the wind. Its

1 For further details concerning the Bromeliacea see Schimper, Die epiphytische Vegetation Amerikas, in Schimper's Botanische Mittheilungen aus den Tropen. Jena, 1891.

absorption takes place entirely through hairs developed upon the leaves.

In addition to such examples of plants which have lost their roots on account of the functions of the roots being assumed by other organs, there are also plants in which the roots represent the sole

FIG. 81.-Taniophyllum Zollingeri with branches adhering to bark. The plant bears a flower and a bud.

vegetative organs.

In Taniophyllium Zollingeri (fig. 81), an epiphytic orchid, the leaves are reduced to minute scales and are of no importance in the nutrition of the plant, that function being transferred to the roots which in the form of flat green ribbons, apply themselves closely to the bark of trees. In this case the roots have assumed the

functions of leaves, while in Tillandsia usneoïdes the leaves have taken on the functions of roots.

The Podostemacea are aquatic plants which live in warm regions attached to rocks in cascades. The stems and leaves are completely absent, the flowers even being produced on the roots. Some of the roots become closely attached to the stones. Others which are green and ribbon-like, float in the stream, and serve for assimilation.

§ 3. Atrophy from lack of nutrition.

In some cases of degeneration, the organs do not lose their functions, but become reduced, merely because adjacent parts rob them of their nourishment. This kind of lack of nutrition which results in local atrophy, must be distinguished from the general limitation of food-supply which is the ultimate cause of all degeneration. The possible amount of food within the reach of any organism is limited, but besides this, the share of the absorbed food obtained by any particular organ or part of an organ may be limited with a resulting atrophy of that organ or part. Atrophy of this kind may be accidental or normal,

1. Parasitic castration.-A good instance of accidental atrophy of this kind is found in Melandryam album where the ravages of a fungus Ustilago antheridarum may produce parasitic castration.1

1 See Giard, La Castration parasitaire in the Bull. Scient. de la France et de la Belgique. 1887, 1888, 1889.

Under the influence of this parasitic fungus which makes its way to the anthers, the stamens of the female flowers assume the form of those in male flowers and in consequence the pistils of these flowers abort from defect in nutrition.

2. Severe or prolonged compression of a limb.-A long continued or forcible compression of a limb results in atrophy of its extremity on account of lack of nutrition from the compression of the bloodvessels.

3. Atrophy of the genitalia in neuter bees.-Lack of nutrition is also the cause of the arrested development of the genitalia normal in neuter bees. The neuters of bees and of some of their allies are females in a state of arrested development. In wasps, humble-bees, and hive-bees, it sometimes occurs that the genitalia of these forms develop sufficiently to be functional, thus resulting in the appearance of small females. In most honeycombs two kinds of cells are formed: in the smaller and more numerous cells are placed the larvæ destined to become neuters, in the larger and less numerous those destined to become queens or perfect females. The food of the two sets of larvæ is different; those in the larger cells are given "royal food" a more nutritious substance. When some of the royal food by an accident gets into a worker cell the sexual organs of that larva are developed so that a small female is formed. In this way as many females as may be desired can be produced,

and when a hive has lost its queen, the worker bees produce another1 (Lacordaire).

Plants afford many instances of degeneration due to defect of nutrition,

4. Atrophy of the superior flowers in Carex.-In the tall spikes of Carex, it frequently happens that the flowers towards the summit are rudimentary, and authorities are agreed in regarding this condition as the result of defect in nutrition.

5. Atrophy of pistils and stamens.-Cases of atrophy of the stamens or pistils normal in species may be given.

In Fritillaria persica the flowers are disposed in bunches. The lower flowers possess six perianth members, two cycles of three stamens each, and a pistil. In the median flowers the pistil is smaller, and rarely capable of being fertilized. In the superior flowers the degeneration is complete, the pistil hardly being formed. It might be shown

1 The transference of a function is not invariably accompanied by degeneration. Thus, in the functional development of an individual's nervous system voluntary acts which have been repeated frequently become reflex actions, and have their seat in a different region of the nervous system-as, for instance, walking and acquired professional dexterities. It has been sought to explain the development of the instincts of species in this way by supposing that frequently repeated voluntary acts have become inherited reflexes. As pathological degeneration in man frequently affects the higher regions of the brain, reflexes and instincts may persist after loss of voluntary action. In the cases of transference of nervous functions to lower centres the higher centres do not degenerate but remain able to acquire new voluntary functions.