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A mutant allele of the maize brittle-7 ( b t l ) locus, brittle-l-mutable (btl-m), was shown genetically and molecularly to result from the insertion of a defective Suppressor-mutator (dSpm) transposable element. An Spm-hybridizing restriction enzyme fragment, which cosegregates with the btl-m allele and is absent from wild-type revertants of btl-m, was identified and cloned. Non-Spm portions of it were used as probes to identify wild-type ( B t l ) cDNAs in an endosperm library. The 4.3-kb btl-m genomic clone contains a 3.3-kb dSpm, which is inserted in an exon and is composed of Spm termini flanking nonQpm sequences. RNA gel blot analyses, using a cloned Btl cDNA probe, indicated that Btl mRNA is present in the endosperm of developing kernels and is absent from embryo or leaf tissues. Several transcripts are produced by btl-m. The deduced translation product from a 1.7-kb Btl cDNA clone has an apparent plastid transit peptide at its amino terminus and sequence similarity to severa1 mitochondrial innerenvelope translocator proteins, suggesting a possible role in amyloplast membrane transport.

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Although international comparisons of average student performance are a staple of U.S. educational debate, little attention has been paid to cross-national differences in the variability of performance. It is often assumed that the performance of U.S. students is unusually variable or that the distribution of U.S. scores is left-skewed – that is, that it has an unusually long ‘tail' of low-scoring students – but data from international studies are rarely brought to bear on these questions. This study used data from the Third International Mathematics and Science Study (TIMSS) to compare the variability of performance in the U.S., Australia, France, Germany, Hong Kong, Korea, and Japan; investigate how this performance variation is distributed within and between classrooms; and explore how well background variables predict performance at both levels. TIMSS shows that the U.S. is not anomalous in terms of the amount, distribution, or prediction of performance variation. Nonetheless, some striking differences appear between countries that are potentially important for both research and policy. In the U.S., Germany, Hong Kong, and Australia, between 42 and 47 percent of score variance was between classrooms. At the other extreme, Japan and Korea both had less than 10 percent of score variance between classrooms. Two-level models (student and classroom) were used to explore the prediction of performance by social background variables in four of these countries (the U.S., Hong Kong, France, and Korea). The final models included only a few variables; TIMSS lacked some important background variables, such as income, and other variables were dropped either because of problems revealed by exploratory data analysis or because of a lack of significance in the models. In all four countries, these sparse models predicted most of the between-classroom score variance (from 59 to 94 percent) but very little of the within-classroom variance. Korea was the only country in which the models predicted more than 5 percent of the within-classroom variance in scores. In the U.S. and Hong Kong, the models predicted about one-third of the total score variance, and almost all of this prediction was attributable to between-classroom differences in background variables. In Korea, only 19 percent of total score variance was predicted by the model, and most of this most of this was attributable to within-classroom variables. Thus, in some instances, countries differ more in terms of the structure and prediction of performance variance than in the simple amount of variance. TIMSS does not provide a clear explanation of these differences, but this paper suggests hypotheses that warrant further investigation.

Did the universe come to be without a cause? In "The Uncaused Beginning of the Universe" Quentin Smith claimed with considerably more confidence than most cosmologists that all doubts that it did are "unfounded." 1 I demurred, 2 troubled by a version of the Principle of Sufficient Reason" (PSR): Nothing comes to be without a cause. As Smith himself implicitly acknowledged, even if the Hawking-Penrose theorems predict a cosmic singularity-Hawking is now trying to persuade everyone that they do not if quantum factors are taken into account 3-this only shows that the universe did not have a physical cause. 4 The existence of a cosmic singularity does not automatically exclude a prior supernatural cause. 5 Nor does quantum physics provide a reason for abandoning PSR, once the concept of cause is properly separated from the concept of a determining cause. 6 Thus while the deliverances of contemporary science may warrant the conclusion that the world came to be without a physical cause, they do not warrant Smith's far stronger conclusion that it came to be without any cause whatsoever. Indeed, given PSR, quite the contrary seems warranted: the universe had a cause-a non-physical cause. Given PSR. But why accept PSR? In his reply to me in these pages, "Can Everything Come to Be Without a Cause," Smith maintains that PSR is not self-evident and that my argument for it fails. We thus have no good reason to accept the principle. And therefore he says (paring down his original claim) it is possible the world came to be causelessly. In Part 1,1 will argue that Smith improperly assumes that if PSR is not self-evident or obvious in his narrowly defined sense, then absent a good argument for the principle it is unwise to accept the principle. In Part 2, I will answer his objections to my argument for PSR. In Part 3, I will