PLATES IV-VICLOSTRIDIUM S O R D E L L I I is one of the six individual clostridia capable of producing gas gangrene in man (MacLennan, 1962). It has been isolated from gangrenous war wounds and has also been described as the causative agent of post-operative gas gangrene and spontaneous peritonitis in man (Sordelli, 1922;Meleney, Humphreys and Carp, 1926-27, 1927; Hall and Gray, 1931 ; Harvey and Meleney, 1944) and gas gangrene in cattle and sheep (Brooks, Sterne and Betty, 1956; Smith, Safford and Hawkins, 1962). MacLennan has even suggested the incorporation of CZ. sordeZZii antitoxin in commercial antisera. However, little is yet known of the toxicology of this clostridium.The lesions in natural and experimental infection and those resulting from the injection of toxic preparations have two main features, oedema and haemorrhage. Dermal necrosis, haemolysis and the production of opacity in egg yolk-or serum-containing media are other effects that can be caused by this organism. MacLennan summarised the available data on the biologically active products of CI. sordellii as follows. These are (1) a major lethal toxin described as potent, thermolabile, non-haernolytic and producing in laboratory animals severe gelatinous oedema; (2) a non-toxic lecithinase or phospholipase C , which produces a Nagler reaction on lecithovitellin agar plates; (3) an oxygen-labile haemolysin of the same type as the oxygen-labile haemolysins of CI. welchii, CI. septicum and CI. oedematiens ; (4) a fibrinolysin; and (5) a collagenase, the existence of which needs confirmation. The biological effects of the toxins and other products of CI. sordellii have, however, not been analysed in the same detailed manner as those of CI. welchii and CI. oedematiens.This report summarises evidence for the existence in CZ. sordellii of a hitherto undescribed toxin that produces characteristic haemorrhages in the skin and deeper tissues and dermal necrosis in experimental animals. Evidence for the existence of a deoxyribonuclease and of phospholipase A and B activity in toxic extracts was also obtained in this study. MATERIALS AND METHODSStrain of CI. sordellii. Strain CN3903 of the Wellcome Research Laboratories was used. This strain did not produce phospholipase C , as judged from tests (van Heyningen, 1941) with cooked meat culture filtrates and saline extracts of cells.Medium. The following medium was found to produce profuse growth at 37°C:'' Oxoid " Bacteriological peptone, 3 per cent.; sodium B-glycerophosphate, 1 per cent. The medium was sterilised by autoclaving at 15 lb. pressure (121°C) for 15 min. The pH

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Amplified fragment length polymorphism (AFLP) markers were used to investigate the relationships among Polystachya accessions from a group of closely related pantropical tetraploids. Before starting with the fingerprinting analyses, the polyploid accessions were first included in a phylogenetic analysis using low-copy nuclear DNA data to establish their relationships, which confirmed that they belonged to a species group of closely related allotetraploids. Neo-and Palaeotropical polyploid accessions formed two hybrid clades with apparently independent origins. Sampling for the AFLP analyses included single accessions from much of the range of the genus and populations from Costa Rica (CR) and Sri Lanka (SL) to compare population structure and genetic diversity in these two areas in more detail. A splits graph of the complete AFLP data showed three major clusters corresponding to three sources of population sampling (P. concreta, SL; P. foliosa, CR; P. masayensis, CR), with individual accessions from Africa and Indian Ocean islands showing a closer relationship to P. concreta from SL than to the two CR species. Individual accessions from the Neotropics occurred in more isolated positions in the splits network, with little resolution. Some P. foliosa accessions clustered with P. masayensis, suggesting some hybridization between the two species, and this was confirmed by Bayesian structure analysis. However, the splits network, structure and analyses of molecular variance indicated a generally high level of genetic divergence between the two CR species, despite their recent hybrid origin, occurrence in largely the same localities and occasional hybridization. Polystachya foliosa from CR had a higher degree of population-level genetic structure (FST = 0.291) than P. masayensis from CR (FST = 0.161) and P. concreta from SL (FST = 0.138), possibly because of its occurrence within a larger and more environmentally diverse continuous range than the other two species. Genetic divergence between Neo-and Palaeotropical members of the pantropical tetraploid group of Polystachya and the nonmonophyly of P. concreta suggested that P. concreta s.l. should be split and the use of this epithet should be confined to the Neotropics (the type is from Martinique). Other names should be used in Africa and the Asian tropics.