128 Botany 



and methods, and takes account of all the researches that have concerned them- 

 selves directly with indicators or have employed 'the methods of instrument, 

 quadrat, and succession in obtaining what are essentially indicator values. A sec- 

 tion is devoted to a consideration of the indicator concept and a brief account 

 is given of the special materials used in the book. 



The bases and criteria of indicators are treated in detail. The former com- 

 prise physical, physiological, associational, successional, and experimental bases. 

 The fundamental criteria are life-forms, which are regarded as comprising vege- 

 tation-forms, habitat-forms, growth-forms, and competition-forms, and the kinds 

 of plant communities. A new and consistent classification of habitat-forms is 

 also proposed. The kinds of indicators are considered in much detail under the 

 four heads, factor, process, practice, and paleic indicators. The first comprises 

 the indicators of physical factors and factor-complexes; the second are those of 

 fire, cultivation, grazing, etc. ; practice indicators have to do with agriculture, 

 grazing, and forestry. Paleic indicators include all of these in some degree, 

 but they warrant special 'treatment by virtue of their paleontologic correlations. 



A concise but consistent account of the climax formations of the West has 

 been given for the first time. The various associations and formations are treated 

 with particular reference to their indicator significance, and hence no attempt has 

 been made to give a detailed account of them. The nature, extent, unity, and 

 associations of each formation are first discussed, after which the associations are 

 treated with reference to their nature, extent, consociations, sequence of domi- 

 nance, societies, and clans. 



A chapter each is devoted to agricultural, grazing, and forest indicators. Under 

 agricultural indicators are considered land classification, climatic cycles, types of 

 farming, kinds and types of crops, and cycles of production. The chapter on 

 grazing indicators is devoted to a comprehensive account of grazing types as 

 indicators, carrying capacity, over-grazing, range improvement, and the essentials 

 of a grazing policy. Under forest indicators are discussed forest types, forest 

 sites, climatic and edaphic indicators and planting indicators of afforestation and 

 reforestation. The relation of climatic cycles to agriculture, grazing, and forestry 

 has been considered at some length in each case. 



No. 248. BRITTON, N. L., and J. N. ROSE. The Cactaceae. Descriptions and Illus- 

 trations of Plants of the Cactus Family. Quarto. 



Vol. 1. vn+236 pages, 36 plates, 302 text figures. Published 1919. Price $18.00. 

 Vol. II. In press. 

 Vol. III. In press. 



This is a monographic treatment of the Cactus family, of which there are more 

 than 1,000 species confined to North and South America. The work has been 

 carried on in cooperation with the New York Botanical Gardens, the U. S. National 

 Museum, and the U. S. Department of Agriculture. Extensive explorations have 

 been made by the authors in the deserts of Mexico, the United States, South 

 America, and the West Indies where the plants were studied as individuals, and 

 observations were made on form, habit, habitat, and their relations to other species. 



The Cacti as treated in Volume I consist of a single order, Cactales, and of a 

 single family, the Cactaceae; they are divided into three tribes, Pereskieae, Opun- 

 tieae, and Cereae. This volume contains the treatment of the first two tribes. 

 The third tribe is to be treated in subsequent volumes. 



The tribe Pereskieae contains the single genus, Pcreskia, in which 19 species 

 are described. The second tribe, Opuntieae, contains 7 genera, Tacinga and 

 Grusonia, each with a single species, Pterocactus with 4, Maihuenia with 5, 

 Nopalea with 8, Pereskiopsis with 10, and Opuntia with 264, grouped into 3 sub- 

 genera and 46 series. 



The genera and species are described in detail with full synonymy. One new 

 genus (Tacinga} and 43 new species are described. All of the genera have been 

 illustrated and of the 312 species 267 are represented by one or more illustrations. 

 Among the illustrations are 2& colored plates. 



