The magnetic susceptibilities of metallic oxides, with special reference to those of chromium and manganese

Different workers report widely divergent results for tho magnetic susceptibilities of the transition metals. It has now been shown that, if the best values for the susceptibility are taken, the magnetic moment, as calculated from the Curie law, gives values which are of no theoretical significance, but application of Weiss's modification of this law to the oxides of chromium and manganese gives values for the magnetic moment which are in accord with theory and enable magnetic measurements to be used for the evaluation of the correct formulae of oxides. The formulae of the oxides of manganese are discussed, and the occurrence of quadrivalent chromium in a hydrated dioxide of that metal established. The magnetic susceptibility of tho various stages of decomposition of chromium trioxide has been measured, and it has been found that there is little change in the magnetic susceptibility with variation of composition in non-stoichciometric oxides. The Cr203 non-stoichciometric oxide is ferromagnetic. Samples of chromic oxide prepared by different methods have slightly different susceptibility values. It is suggested that these differences are due to the presence of impurities and, in particular, to small amounts of chemisorbed gaseous elements, The adsorption of oxygen or of hydrogen at 440° on this oxide causes definite variation in tho susceptibility value. High-temperature evacuation likewise causes a considerable fall tn the susceptibility of chromic oxide. It is suggested that activated adsorption on oxides is connected with reduction of chemisorbed oxygen, and the use of magnetic measurements is recommended as a means of following surface chemical processes on oxides

Sources of variation in self-incompatibility in the Australian forest tree, Eucalyptus globulus

† Background and Aims One of the major factors affecting the outcrossing rate in Eucalyptus globulus is thought to be the inherent self-incompatibility (SI) level of the female tree. SI in this species is mainly due to late-acting pre- and post-zygotic mechanisms operating in the ovary, and not S alleles. This study aimed to assess the phenotypic variation in SI levels within E. globulus and determine its genetic control and stability across pollination techniques, sites and seasons. † Methods SI levels were estimated for 105 genotypes originating from across the geographical range of E. globulus over multiple years of crossing. Separate grafted trees of some genotypes growing at the same and different sites allowed the genetic basis of the variation in SI to be tested and its stability across sites and seasons to be determined. The SI level of a tree was measured as the relative reduction in seeds obtained per flower pollinated following selfing compared with outcross pollinations. Thus, if seed set is the same, SI is 0 %, and if no self seed is set, SI is 100 %. † Key Results The average SI in E. globulus was 91% and genotypes ranged from 8 to 100% SI. Most genotypes (.75 %) had SI levels .90 %. There were highly significant differences between genotypes and the within-site broad-sense heritability of percentage SI was high (H2 ¼ 0.80+0.13). However, there was evidence that growing site, and to a lesser extent season, can affect the expression of SI levels. Trees with low reproductive loads produced relatively more seed from selfed flowers. †Conclusions There is a strong genetic basis to the phenotypic variation in SI in E. globulus within a site. However, the level of SI was affected, but to a lesser extent, by the environment, which in part may reflect the higher probability of selfed zygotes surviving on sites or in seasons where competition for resources is less