tropics, especially in South America, plants are much exposed to the ravages of leaf-eating ants (Atta). In order to protect themselves, they provide other kinds of ants with shelter and nourishment, and this necessarily entails several modifications.

FIG. 48.-Part of a leaf of Acacia sphaerocephala (after Schimper, Die Wechselbeziehungen zwischen Pflanzen und Ameisen im tropischen Amerika. Fasc. 1 of Schimper's botanische Mittheilungen aus den Tropen. Jena, 1888).

In Acacia sphaerocephala (fig. 48), for instance, the blades of the leaves are bipinnated and the proximal leaflets terminate in small cavities filled with a nutritive secretion. The stipules, which no longer contain chlorophyll, are modified into hollow thorns in which

the ants live and obtain nutriment, not only at the ends of the leaflets, but also in a thorny gland which is situated upon the petiole.

5. Adaptation to drought. -In places where rain seldom falls, plants are provided with natural reservoirs of water.

These

reservoirs are situated either in the roots or the stems and occasionally in the leaves. Where the leaves are fleshy, these reservoir leaves are generally very simple in forma

FIG. 49.-Growing point of Semper- tion. Those of Sempervi

vivum arachnoideum.

vum and of several other

genera arise directly from the primordial, nondifferentiated leaf,

and there is no differentiation into hypopod, epipod and petiole (fig. See further

49).

on (fig. 73), p. 236 (Sempervivum tec

torum).

FIG. 50.-Branch of Caragana.

6. Adaptation to defence against herbivorous animals.-Thorns are an adaptation which serve as a protection against herbivorous animals. They

are derived from the modifications of various parts of the plant, either the roots, stems, leaves, or even of the floral stems.

This modification is always accompanied by some degeneration; the thorn, which is quite hard, ex

FIG. 51.-Mamillaria elephantidens (after Lemaire ? The figure is taken from Goebel, Pflanzenbiologische Schilderungen, vol. i., p. 71).

cepting at the point, is made up of thick-walled cells from which the protoplasm has disappeared.

Leaf thorns arise from the modification of various parts of the leaves-either of the stipules (as in Caragana), the petioles (id.) (fig. 50), or of the

blade (as in Ilex). In each case the leaf partially retains its assimilating function and its chlorophyll.

In other plants, however, and especially in Cacti, and the fleshy-leaved Euphorbias, the leaves exhibit further evidences of degeneration, their function being exclusively one of defence (fig. 51).

CHAPTER II

IN THE EVOLUTION OF INSTITUTIONS ALL MODIFICATION IS NECESSARILY ACCOMPANIED BY

DEGENERATION

THE distinction we have drawn between the homodynamic organs of an organism, and the homologous organs of organisms belonging to other species, is not applicable in sociology, as we have already pointed out in the introduction. Institutions, however, may be regarded from two distinct standpoints from a statical point of view, as they exist in the same society, and from the dynamical point of view, as existing from epoch to epoch, and from society to society. In both cases, we shall arrive at the same conclusion as in biology, that all modification entails degeneration.

In order to demonstrate this we will examine in succession the modifications undergone by the principal types of financial organizations now exist

ing in Europe, and the most important stages in the evolution of landed property amongst various peoples.

§ 1.-Modifications of similar institutions in the same society.

The financial organization of European towns and states has undergone very important changes since the middle ages. Taxes and duties have attained a now universal importance, as substitution for the revenue from crown lands, which constituted the principal, if not the only, resources of the sovereigns of the feudal ages.1

1There are three stages in the evolution of financial systems in countries (such as England, for instance) where the question of finance has been most successfully dealt with.

1. The Feudal System, wherein the king had no separate revenue apart from the nation, and wherein the revenue of the sovereign was principally derived from crown land, the cultivation and administration of which was carried on as a source of private income to the king.

2. The Co-existence of the Feudal System and the Modern System, viz., the disappearance of personally held land and its attendant institutions, the development of the public property of the State or Township, and the imposition of duties and taxes.

3. The Modern System, viz., the complete separation of the personal property of the sovereign from the property of the nation, the increasing importance of taxes and duties, and the almost complete disappearance of State and town lands. Industries taken over by the State—such as railways, postal and telegraphic arrangements, etc.—and by the towns-such as gas, water, etc.-constitute monopolies, and are no longer subjected to the law of competition which is always active in private business. —WAGNER.