STUDIES IN THE LEGUMINOSAE. III. CYTOLOGICAL STUDIES OF LONCHOCARPUS AND DERRIS SPECIES

IN THE LAST two decades Derris Lour. and Lonchocarpus HBK have assumed an important commercial position as sources of the insecticide rotenone, and have been subjects of a great number of taxonomic, chemical and agronomic investigations. However, there are few available reports of cytological studies. Chromosome numbers of 2n20 for Derris elliptica and 2n -_ 22 for D. malaccensis were reported by Heyn (1938), who expected to find further differences in number in other species of the same genus. Skalinska (1945) found a 2n number of 22 for D. elliptica; the present study confirms this as the correct number. Cytological studies involving nine species of Lonchocarpus and four species of Derris will be considered here. Lonchocarpus and Derris are continuously recurring sources of taxonomic debate. The two genera are combined under Derris by MacBride (1943), separated by Killip and Smith (1930), Krukoff and Smith (1937), and Hermann (1947). Bentham (1860) in setting up the tribe Dalbergieae suggested that Lonchocarpus, Pongamia, Piscidia, and Muellera should probably be combined under Derris; yet he retained them as separate genera. The principal reason for retaining both Lonchocarpus and Derris is apparently geographical, Louichocarpus being the new world, Derris the old world genus. However, species of each have been described from both regions. Failure of collectors to find flowering or fruiting specimens of various high rotenone species has resulted in descriptions from leaf characters only, so that the nomenclature of these species is especially confusing. For example, L. utilis A. C. Smith, described from a sterile specimen originally determined as L. nicou (Aubl.) DC., is now referred to L. utilis A. C. Smith, L. nicou var. utilis (A. C. Smith) Hermann, or Derris utilis (A. C. Smith) MacBride. Cytological study may aid in clarifying some of the taxonomic problems, as well as contribute useful information toward practical breeding problems. Lonchocarpus utilis, L. nicou, L. urucu, Derris elliptica and D. malaccensis are the principal specific sources of commercial rotenone. Of the two genera Lonchocarpus is considered the better source (Jones, 1942). Various species of no commercial importance are strikingly ornamental in their native habitats or under cultivation. L. punctatus from Venezuela and L. Dominguensis in I Received for publication December 8, 1948. Publication No. 2, Journal Series from the Atkins Garden and Research Laboratory of Harvard University, Soledad, Cienfuegos, Cuba. The problem was supported by the National Research Council and The Bussey Institution of Harvard University. The author is indebted to Dr. Karl Sax, Dr. P. C. Mangelsdorf, Dr. 0. E. White and Dr. A. G. Kevorkian for suggestions and criticisms. Cuba are usually found along stream banks where they produce an abundance of showy, rose-colored, perfumed flowers. Nigerian natives use L. cyanescens in making an indigo dye. Desirable clones of both genera are usually propagated by means of cuttings, since the species root easily. In this manner, under constant environmental conditions, the rotenone percentage of the original plant is preserved. Thus well-known clones with widely distributed members have arisen. MATERIALS AND METHODS.-All collections of Lonchocarpus and Derris included in this study are from permanent plantings at the Atkins Garden and Research Laboratory of Harvard University, Cienfuegos, Cuba. Original source of material, chromosome number, general distribution of the species and the author's collection number are included in table 1. The identity of the collections has been checked, in so far as possible, by comparison with specimens in the herbarium of the Arnold Arboretum and Gray Herbarium; triplicate specimens have been deposited in the Gray Herbarium, National Herbarium and Atkins Garden and Research Laboratory. It was not possible to make herbarium specimens of L. utilis, D. malaccensis, or the various clones of D. elliptica (GM 1, 2, 5, 7 and "Panama") because the cuttings from which chromosome counts were made had not grown sufficiently. Since these cuttings were obtained from clones which are under experimental study for rotenone content, and which have been subject of some of the taxonomic studies, their identities were accepted as reliable. Somatic chromosome determinations were made from acetic orcein smears of young leaves, petals, or root-tips, pretreated for 1 hr. with a saturated solution of paradichlorobenzene (Meyer, 1945) and fixed in Carnoy's solution. Meiotic studies were made on pollen mother cells smeared in acetic orcein without previous fixation. Camera lucida drawings (fig. 1-11) are reproduced at magnification of ca. 2000. OBSERVATIONS.-1.-L. cyanescens, n 11, 2n 22 (fig. 1, 2). Univalents were occasionally seen in metaphase I divis'ion, but anaphase separation was apparently regular. Pollen counts showed 98 per cent of the grains to be full. Although pollen development was apparently normal, the three plants observed are all sterile; they flowered four times in 11 months but no fruit set. Numerous attempts were made to force fruiting artificially: stigmas were bruised, pollen was transferred from other flowers on the same plant, from different plants of the same species, and from L. violaceus. None of these pollinations was successful.