Time of initiation of the barley endosperm response to gibberellin A3, gibberellin A14 and kaurene

Summary Gibberellin A₁₄ and kaurene, precursors of gibberellin A₃, are active in the barley endosperm reducing-sugar assay, but require longer incubation periods for activity to be observed than does GA₃. This finding shows that the incubation period must be considered when determining whether a compound is active in this assay. The longer incubation periods required by GA₁₄ and kaurene may reflect reduced rates of penetration, or reduced activity within the cell, or the time required for conversion to a physiologically active form.     

Population structure of some pond Microcrustacea

Summary The aestival species composition of microcrustacea of eight ponds in southwestern Kansas is described. Two benthic Ostracoda and three planktonic Copepoda and eight planktonic Cladocera were collected.On the whole, the Copepoda were more abundant than the Cladocera. Patterns of relative abundance varied from week to week and were more varied than the patterns described for the limnetic zone of lakes. There were two or three copepods in each pond. Except for one pond which had no Cladocera, there were two to five species of Cladocera per pond.There were fourteen significant affinities among the plankters. Two species showed no affinity. The relationships among four recurrent groups were established. Group I contained one cyclopoid, one calanoid and two cladocerans, a pattern not unlike the typical limnetic community.The population structure of each species that occurred in more that one pond was analyzed by analysis of variance. Significant differences between the ponds occurred from various species in per cent copepodids in the population, per cent females with eggs, and the number of eggs per egg sac. There was no significant difference among the ponds regarding the mean number of eggs per ovigerous female for any cladoceran.Interactions among the species and faunal characteristics of the ponds are discussed in relation to the environmental characteristics of the ponds.

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Zusammenfassung Die Zusammensetzung der estivalen Arten von Mikrocrustacean von acht Teichen im Südwesten von Kansas wird beschrieben. Zwei benthische Ostracoden, drei planktonische Copepoden und acht planktonische Cladoceren wurden gefunden.Die Copepoden waren im allgemeinen häufiger als die Cladoceren. Die Schemen der relativen Anzahl wechselten von Woche zu Woche und waren unterschiedlicher als die Schemen für die limnische Seezone. Zwei oder drei Copepoden, sowie zwei bis fünf Arten von Cladoceren kamen in jedem Teich vor, ausser in einem Teich, in dem keine Cladoceren gefunden wurden.Vierzehn wichtige Übereinstimmungen wurden unter den Planktonern gefunden. Zwei Arten zeigten keine Affinität. Der Zusammenhang zwischen vier wiederkehrenden Gruppen wurden nachgewiesen. Gruppe I enthielt einen Cyclopoiden, einen Calanoiden und zwei Cladoceren, ein für typisch limnische Gemeinschaften übliches Schema.Die Bevölkerungsstruktur jeder Art, die in mehr als einem Teich vorkam, wurde durch Streuungsanalyse untersucht. Es wurden signifikante Unterschiede im Prozentsatz der Copepoden: Bevölkerung, der Weibchen mit Eiern, der Anzahl Eier im Brutraum für die verschiedenen Arten zwischen den Teichen gefunden. Keine signifikanten Unterschiede wurden in der Anzahl Eier pro eitragendem Weibchen der Cladoceren zwischen den Teichen gefunden.Auch der Einfluss der Umweltfaktoren der Teiche auf die Arten und auf die Fauna des Teiches wurde untersucht.

     

Ionic Current Measurements in the Squid Giant Axon Membrane

The concepts, experiments, and interpretations of ionic current measurements after a step change of the squid axon membrane potential require the potential to be constant for the duration and the membrane area measured. An experimental approach to this ideal has been developed. Electrometer, operational, and control amplifiers produce the step potential between internal micropipette and external potential electrodes within 40 microseconds and a few millivolts. With an internal current electrode effective resistance of 2 ohm cm.², the membrane potential and current may be constant within a few millivolts and 10 per cent out to near the electrode ends. The maximum membrane current patterns of the best axons are several times larger but of the type described by Cole and analyzed by Hodgkin and Huxley when the change of potential is adequately controlled. The occasional obvious distortions are attributed to the marginal adequacy of potential control to be expected from the characteristics of the current electrodes and the axon. Improvements are expected only to increase stability and accuracy. No reason has been found either to question the qualitative characteristics of the early measurements or to so discredit the analyses made of them.