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IT HAS LONG been known that Saccharomyces cerevisiae ferments galactose by an adaptive enzyme produced in the cell during the course of a few hours in the absence of cell division. Winge and Roberts (1948) have studied a culture of S. Chevalieri which ferments galactose by "long-term" adaptation which occurs after cells have grown from 3-14 days in a medium containing galactose. After the adaptation, the fermentation itself occurs at a rapid rate. They state that "long-term" adaptation of S. Chevalieri to galactose does not involve a shift in the population (mutation followed by selection) but is an adaptation of the entire original population. They consider the delay an indication of the time required by the cells to build up galactozymase to a sufficiently high concentration to make it demonstrable. They made hybrids between these two species and found a regular segregation of rapidly fermenting (1-2 days) to "long-term" adapting (3-14 days) clones from each ascus, provided the ascospores were isolated in beer wort, a medium containing considerable amounts of maltose, but lacking galactose. If the ascospores were isolated in galactose broth, all four spores from each ascus fermented galactose immediately (1-2 days). However, they used only asci in which all four spores germinated and the possibility exists that some nonutilizers of galactose may have failed to grow in maltose. They described a series of experiments in which they deadapted and readapted galactose fermenting cultures and denied the significance of mutation as a factor in this process. Extended genetical analyses bv Lindegren (1949) have established the allelism of a single pair of galactose genes (G/g) in Saccharomyces. One of these alleles (G) controls the rapid fermentation of galactose while cells carrying the other (g) do not effect detectable fermentation of galactose under the conditions of the Durham tube fermentation test. (Occasional irregularities in which an excess of fermenter (G G G g) or an excess of nonfermenter (g g g G) alleles were obtained from single asci have been interpreted as the result of conversion of alleles in the heterozygote.) We have discovered occasional cultures in our pedigrees which resemble the cultures of S. Chevalieri described by Winge and Roberts, by fermenting galactose after a long exposure involving growth; the present paper deals with the behavior of these unusual "slow" fermenters of galactose. We have concluded that this involves mutation from the g to the G allele followed by selection of the mutant G population in the presence of galactose.

1. The morphology and cytology of the sex organs of a new species of Phytophthora, P. himalayensis Dastur, have been studied and compared with those of P. erythroseptica, the only other amphigynous Phytophthora investigated so far. 2. Accounts of some workers, who claimed that the amphigynous relation of the sex organs is an illusion resulting from an encircling of the male around the female gametangium, are considered, and the view is held here that the oogonial incept does actually penetrate the antheridium. 3. Nuclear behavior in the male and female sex organs is described from the earliest stages to the formation of the oospore. The antheridial nuclei are few, being generally four, sometimes seven or eight. The oogonial nuclei are variable in number; not more than sixty have been seen in one oogonium. In both organs a degeneration of nuclei occurs during which only one nucleus from the oogonium and one (generally) from the antheridium survive. These privileged nuclei function in fertilization. The elo...

Durch Gefriertrocknung nachAltmann-Gersh wurden zytologische Praparate von einer genetisch gepruften polyploiden Serie von Hefe hergestellt. Die gemessenen Werte fur Kern- und Zellgrossen stimmen in der theoretisch erwarteten Weise mit dem Grade der Polyploidie uberein. Damit ist eine von hoheren Organismen bekannte zytologische Erscheinung zum erstenmal fur Mikroorganismen demonstriert.

HAPLOPHASE yeasts capable of fermenting galactose ordinarily produce gas in from sixteen to thirty-six hours at 30° C. after inoculation into nutrient medium containing galactose. Winge and Roberts1 studied clones which fermented the sugar in from three to fourteen days after they were seeded in galactose yeastants to the time required by the cells in the haploid popu extract medium. Following the adaptation period, however, the rate of fermentation was identical with that of ordinary galactose-fermenting yeasts. In their analyses, they found that two haploid segregants from asci heterozygous for galactose fermentation were the ordinary fast fermenters and the other two were ‘long-term’ adapting clones. They attributed the delay in fermentation of the ‘long-term’ adapting segreglation to build up galactozymase to a concentration sufficient for the detection of its presence. The regular segregations of fast/'long-term’ adapting phenotypes among the haploid progeny were offered as proof that delayed fermentation of galactose is controlled by a specific allele. Such originally 2: 2 fast/'long-term’ tetrads were transformed into 4: 0 fast/'long-term’ ratios by extended cultivation in galactose yeast extract medium. Winge and Roberts considered that under these conditions there was no change in the population but merely a ‘long-term’ adaptation of the entire population. In proposing this view, they denied the occurrence of mutations as a factor operative in the ‘long-term’ adaptation, and held that de-adaptation of an adapted clone, as well as its subsequent re-adaptation to galactose, were effected through a modification.

GENETICAL experiments by Ephrussi and co-workers1 have adequately demonstrated the existence of extra-chromosomal factors determining the cytochrome oxidase and succino-dehydrogenase activities of yeast clones analysed by them. A particulate nature was ascribed to these factors, and their identity with the mitochondria was suggested in view of the well-known association of the enzymes concerned with these bodies; however, no direct observations on the behaviour of the mitochondria during cell divisions were reported.

Tetrad analysis, the direct genetical characterization of the segregation products of meiosis, has frequently revealed the occurrence of ratios differing from the 1:1 gametic segregations implicit in the postulates of classical Mendelian genetics. Although many of these exceptions to regular segregation have been reported in the fungi, which offer advantages for genetical analysis denied to the geneticist studying higher organisms, the bases for inferring such divergent segregations were not beyond criticism. Previous workers using the fungi as genetic material investigated inadequately marked stocks (generally only one marker was used) and the deduction of truly non-Mendelian ratios was therefore rendered ambiguous by the possible occurrences of chromosomal aberrations. The few markers used were not sufficient to establish hybridity of the stocks analyzed, and, usually being morphological, introduced obvious difficulties in diagnosing the segregants with accuracy. The occurrence of mutations in the segregants during vegetative growth prior to diagnosis was not excluded as a possible cause obscuring an initially Mendelian segregation. The experiments reported in this paper were designed with the above considerations in view and present data eliminating the questionable features involved in evaluating non-Mendelian inheritance. In the tetrad analyses of the five hybrids