=268. The direction of migration= is determinate, except in the case of those distributive agents which act constantly in the same direction. The general tendency is, of course, forward, the lines of movement radiating in all directions from the parent area. This is well illustrated by the operation of winds which blow from any quarter. In the case of the constant winds, migration takes a more or less definite direction, the latter being determined to a large degree by the fruiting period of any particular species. In this connection, it must be kept clearly in mind that the position of new areas with reference to the original home of a species does not necessarily indicate the direction of migration, as the disseminules may have been carried to numerous other places in which ecesis was impossible. The local distribution of zoochorous species is of necessity indeterminate, though distant migration follows the pathways of migratory birds and animals. In so far as dissemination by man takes place along great commercial routes, or along highways, it is determinate. In ponds, lakes, and other bodies of standing water, migration may occur in all directions, but in ocean currents, streams, etc., the movement is determinate, except in the case of motile species. The dissemination of plants by slopes, glaciers, etc., is local and definite, while propulsion is in the highest degree indeterminate. Migration by growth is equally indefinite, with the exception that hydrotropism and chemotropism result in a radiate movement away from the mass, while propulsion throws seeds indifferently into or away from the species-mass. From the above it will be seen that distant migration may take place by means of water, wind, animals or man, and, since all these agents act in a more or less definite direction over great distances, that it will be in some degree determinate. On the other hand, local migration will as regularly be indeterminate, except in the case of streams and slopes. The direction of migration, then, is controlled by these distributive agents, and the limit of migration is determined by the intensity and duration of the agent, as well as by the character of the space through which the latter operates. _ECESIS_ =269. Concept.= By the term ecesis is designated the series of phenomena exhibited by an invading disseminule from the time it enters a new formation until it becomes thoroughly established there. In a word, ecesis is the adjustment of a plant to a new habitat. It comprises the whole process covered more or less incompletely by acclimatization, naturalization, accommodation, etc. It is the decisive factor in invasion, inasmuch as migration is entirely ineffective without it, and is of great value in indicating the presence and direction of migration in a great number of species where the disseminule is too minute to be detected or too little specialized to be recognizable.