Genetic distance between populations

Summary Three strains of McIntosh apple (Malus domestica Borkh.) with growth habits ranging from the standard parent type to extremely compact (dwarf) were grown in vitro as meristem-tip cultures on Murashige and Skoog medium containing a range of concentrations of benzyladenine (BA). All strains exhibited a similar optima (3 to 6 M BA) for maximum shoot proliferation and culture weight increase. However, tolerance to supra-optimal concentration of this cytokinin was related to growth habit. For example, at 10 M BA shoot production rates as a percent of the maximum rates were 90%, 20% and zero for the extreme compact, moderate compact and standard strains, respectively. Comparisons among field trees and meristem-tip cultures of all three strains revealed similarities in growth and development.Summerland Research Station, Contribution No. 532     

Maintenance of the Adult Rat Superior Cervical Ganglion In Vitro: Comparison of Organ and Explant Culture Systems

Abstract: Concentrations of selected intermediates of energy metabolism whole rat superior cervical ganglia maintained in vitro by an organ culture technique were compared with values measured in small slices of this maintained under essentially the same conditions. Rates of incorporation [³H]leucine into trichloroacetic acid-precipitable material in whole ganglia mained constant for at least 48 h: however, the oxidation-reduction state tissue as indexed by (NAD):(NADH) ratios calculated from measured amounts of lactate and pyruvate decreased more than 50% within ³h in vitro . Ganglion explants prepared by cutting the tissue into ³⁰⁰-pm transverse sections played (NAD):(NADH) ratios that were about three times greater than noted in whole ganglia maintained in vitro for the same period of time. explants contained significantly higher concentrations of pyruvate and α-ketoglutarate than whole ganglia maintained in culture. Maintenance of vorable metabolic state may support the extensive growth of neurites seen explant cultures of superior cervical ganglia. Outgrowth of processes containing catecholamines could be detected readily in explant cultures of ganglia adult rats; however, this was somewhat slower and less consistent than growth observed in explants from neonatal rats. Outgrowth of neurites adult ganglia was minimal without the addition of Nerve Growth Factor.     

Oxygen availability,redox and the distribution of some Turbellaria Schizorhynchidae and other forms

Records from a considerable number of meiofaunal samples are reexamined in relation to the depth within sediment distribution of various taxa especially Schizorhynchidae and the main turbellarian orders.Frequency and density records in samples with particular oxygen flow rates and redox potentials confirm that the ranges of Schizochilus, Proschizorhynchus and Neoschizorhynchus spp. within these factors may help account for congeneric occurrence within cores. However, statistical analysis of the records is seldom able to confirm apparent differences. There is, for example, a statistically significant difference in distribution in relation to redox potential between the red schizorhynchians Pseudoschizorhynchides ruber, Diascorhynchus rubrus and the red acoelan Paratomella rubra but not in relation to oxygen availability and depth within sediment. On one beach Gnathostomula aff. paradoxa was found at Eh and O₂ availability values under which it must be assumed to be living anaerobically.Contingency and other analyses are extended to differences between higher taxa and the results discussed in relation to habitat evolution of the Turbellaria. The suggestion that structural complexity of turbellarians has increased with increased oxygenation of the environment is tentatively supported.     

Zoogeographical distribution of Southeast Asian freshwater Calanoida

This paper reviews the systematic status and geographical distribution of 30 odd species of freshwater calanoid copepods in Southeast Asia. Three regions are delineated based on the diversity and abundance of these organisms; Region I being the Southasiatic element, Region II the attenuated belt of copepods and Region III rich in endemic species. The implication of a north-south diminishing of copepod species to inland fisheries is postulated.     

T-tubes in cultured mammalian myocardial cells

Summary T-tubes are among the last structural elements of the mammalian myocyte to develop in vivo. We were able to identify T-tubes in early cultures of neonatal rat myocytes. Ventricles were excised from 3- to 4-day-old neonatal rats, incubated overnight in cold trypsin, and treated with sequential changes of collagenase-hyaluronidase. Fractions of cells isolated in this manner were pooled and cultured in plastic petri dishes. In cells prepared for transmission electron microscopy, T-tubes were observed at the cell periphery of cultured myocytes, but were more difficult to identify as the cultures aged and became overgrown by fibroblasts. T-tubes were identified by virtue of their continuity with the sarcolemma, their relatively large diameter, and their regular entry at the level of the Z line. Even at optimal culture ages, T-tubes were not present in every myocyte. At the times T-tubes could be located, myocytes were beating and had begun to establish intercalated discs and gap junctions. The de novo formation of T-tubes in cultured myocytes of neonatal rat heart reflects a duplication of in vivo differentiation by the cultured myocyte. The appropriateness of cultured myocytes in the study of the development and physiology of the heart is emphasized by the in vitro formation of T-tubes.Supported by research grants from the Muscular Dystrophy Association, Inc., The Schlieder Foundation, and USPH-Training Grant HL 07098-04. The authors are indebted to Philip Constantin for assistance in dissociating and culturing heart tissue.     

The genusPicris (Asteraceae,Lactuceae) in Tropical Africa

Three species of the genusPicris L. are native in Tropical Africa:P. abyssinica Sch. Bip. (Ethiopia),P. xylopoda Lack, spec. nova (Nigeria, Ethiopia) andP. humilis DC. (Senegal, Mali). There are indications that the two perennial species,P. abyssinica andP. xylopoda, are related to and have evolved from a primitive Central Asiatic stock in a manner parallel to many African species ofCrepis L.P. humilis, on the other hand, is a small annual plant with a high number of derived characters. The introduced species of European origin growing south of the Sahara are briefly mentioned.     

The condensed tannins of pasture legume species

Condensed tannins have been isolated from legume pasture species and purified by gel chromatography on Sephadex G-50 and LH-20 media. Molecular size di