A study of methods for the classification of bottom deposits of natural waters
The study of the role of bottom sediments of rivers and maturation ponds in the purification of polluted waters which flow over them has been handicapped by lack of suitable methods for classifying sediments according to their physical, chemical and biochemical characteristics . Bottom deposits of lakes, rivers and dams may be regarded as soils which have developed under humid and water-logged conditions . The judicious application of the methods developed by soil scientists for the assessment of agricultural soils to the evaluation of certain important characteristics of sediments is therefore a logical development. Pioneering work in this respect was done by ZULLIG (1955) who applied a number of the methods of soil analysis to bottom deposits of eutrophic and oligotrophic lakes in Switzerland and attempted to correlate the results with the degree of trophy of the lake. Both he and OHLE (1955) pointed out that bottom deposits have ion-exchange properties which can contribute to the removal of ions from the water phase into the muds, but neither of these workers attempted to measure the extent to which this occurs quantitatively. In the present study a number of methods used to determine chemical, physical and biochemical properties of soils have been applied to bottom sediments from the Apies River near Pretoria, including samples taken near its origin where it is free from pollution, below the point of discharge of treated effluent from the Pretoria Sewage Works, where considerable pollution occurs and further
Suggested Modified Aluminon Method for Aluminum Determination
Color imetric aluminum methods, appearing in various editions of Standard Methods? have not been satisfactory. None has had the desired accuracy and reproducibility, and all have been subject to interference from iron, chromium, metaphosphate, fluoride, and other ions often present in water supplies. Historically, a gravimetric method did not appear until the sixth edition of Standard Methods. An im-
Indian Fig Cactus (Opuntia Ficus-Indica (L.) Miller) in the Americas: an Uncertain History
Abstract: 
 Opuntia ficus-indica (L.) Miller is a globally important cactus species with a long history of human use. In addition to the importance of O. ficus-indica as a food for humans and livestock, it also has long served a role in the production of cochineal, a once important textile dye. This cactus also is intimately interwoven into the story of Cactoblastis cactorum (Berg) (South American cactus moth), one of the best-known examples of biological weed control. In this regard, O. ficus-indica has been a target weed as well as an unintended host in C. cactorum invasion. Although the distribution and human-assisted movement of this cactus throughout much of the world is well documented, surprisingly little has been written about its history and movement within the Americas. Literature associated with Opuntia and their phytophagous pests in North and South America was examined in an attempt to determine the history of O. ficus-indica in the Americas. Available information suggests with some certainty that O. ficus-indica originated in present-day Mexico, but the timing of its introduction to South America is much less clear. Taxonomic difficulties associated with distinguishing among Opuntia species and the long pre-Columbian history of exchange between South American and Mesoamerican cultures are two primary complicating factors associated with dating the dispersal of this species to South America. Additionally, previous evidence in support of a pre-Columbian introduction to South America relied on questionable identification of insect-based textile dyes. These uncertainties are significant because clearer knowledge of the history of O. ficus-indica introduction to South America could provide a more complete biological and ecological context to efforts at managing this species in its native and introduced ranges, particularly with respect to the threat posed by C. cactorum in North American and Argentinean plantations.