=287.= The methods to be used in the study of invasion are those already described elsewhere. The migration circle is of the first importance because it makes it possible to secure an accurate record of actual movement. Quadrat and transect are valuable, but from their nature they are more serviceable for ecesis than for migration. All of these should be of the permanent type, in order that the fate of invaders may be followed for several years at least. Permanent areas furnish evidence of the changes wrought in the actual vegetation, while denuded ones can serve only to show the potential migration and ecesis of the constituent species. Transition zones and areas are special seats of invasion; they are best studied by means of the belt transect and the ecotone chart. The movement of a line of invaders or of scattered outposts is traced by the use of labeled stakes at the points concerned. It is clear that this method will yield conclusive data in regard to the great invasions between regions, such as the movement of species guilds, the advance of the forest frontier, etc. When invasion is scattered, factor instruments can not be used to advantage, but where the invading line is well marked, or where extra-formational areas occur, a knowledge of the physical factors is a great aid. An invasion that has been completed can not be studied in the manner indicated. A method of comparison must be used, in order to determine the original home of the invaders. For this an exact knowledge of the contiguous formations and of the abundance of the species common to all is a prerequisite. With this as a basis, it is usually a simple task to refer all the species of the formation concerned to their proper place in the groups, indigenous, derived, and adventitious. SUCCESSION