Starting from the general principles of the Ziirich-Montpellier school for the description of vegetation by means of field estimations of abundance, cover etc., the authors criticise the scales adopted by most workers, and some of their interpretations.The following analytical characters of vegetation, and methods of estimation, are discussed: height (layering, recognition of synusiae), peripheral and internal cover, density, abundance, sociability, vitality, fertility, and phenological stage of taxa or layers. The main weakn*lses of the usual scales for estimation of these characters (see list of references) are considered to be: 1. The use of combined scales for estimation of abundance and cover. and of vitality and fertility. 2. The lack of equivalence in the range of values for each class in most of the existing scales. 3. The limited rame of some of the scales, and the absence of provision for more detailed estimaGons. 4. The inexact definition of degrees of abundance and sociability in the Braun-Blanquet scale. 5. The confusion about the concept of density.A number of proposals is made for the use of scales with closer intervals, based on decimal, logarithmic or other systems. These leave less room for personal interpretation, and are more suitable for subsequent calculations and autecological studies. A method of reducing errors by carrying out certain estimations in two successive ste is suggested, e.g. by estimating peripheral and internal percentage cover (Fig. ,$separately and multiplying both values to obtain real cover.The proposed scales have been tested in routine field work by the authors and other workers in a wide range of vegetation types. An example is given of an analysis of Dutch coastal sand dune vegetation in which some of the proposed scales have been applied.The authors hope that their proposals for a more accurate description of vegetation will help to consolidate the basic principles underlying the Braun-Blanquet system of classification.

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Various types of and modern Braun-Blanquet school viewpoints on homogeneity and heterogeneity of vegetation and their causes are discussed. A distinction is made between methodological minimum areas, MMA's (divided into qualitative and quantitative MMA's) and biological minimum areas, BMA's, divided into space, resistance and regeneration minima. Various definitions of the qualitative MMA are reviewed and some methods of analysis are discussed. It was found that the species-area curve of sample plots almost invariably follows the Fisher model, however with superimposed oscillations, which are regarded to represent a number of relative MMA's for each phytocoenosis (stand). These relative MMA's probably correspond to the elements of the compound mosaic pattern of which vegetation normally consists.A method to investigate the various biological minimum areas is expounded and results obtained in chalk grasslands, juniper scrub, oak woods and oligotrophic heath pools are briefly discussed. The species/area curve of BMA's appeared to follow either the Goodall or the Fisher or the Preston model. No saturation of the species number was obtained, not even in the largest stands examined (9 ha). Species numbers of stands were analysed in relation to size and age of the stands and to their degree of isolation. The value of the exponent z of the Preston formula appeared to be an unsuitable measure for the degree of isolation of these habitat islands. This z value was calculated for all species, for various taxonomic groups, including bryophytes and fungi, and for various dissemination types. There is no relation between size of stand, degree of isolation and number of dyschorous resp. eurychorous plants. Species numbers of phytocoenoses are obviously governed mainly by size, age and habitat quality (degree of disturbance).

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