from that of Trillium. The influence of temperature is a very real possibility and is presently under investigation. In conclusion it may be said that for diploid plants a relationship does exist between the minimum mitotic cycle time, the interphase nuclear volume, and the DNA content per cell. Moreover, the relationship is such that if any one of the three cell variables is known, an estimate can be made of the remaining two. Summary.-Experiments were performed to determine the relationship between interphase nuclear volume and DNA content per cell and the minimum mitotic cycle time in several diploid plant species. All measurements were made on meristem cells contained in the terminal 2 mm of the root. The results indicated that linear relationships exist between the interphase nuclear volume and the minimum mitotic cycle time, and between the DNA content per cell and the minimum cycle time. Linearity, however, does not exist if extrapolation is carried out to include the lower forms of life, such as bacteria and viruses. The relationships are to some extent independent of chromosome number and the amount of DNA per chromosome. The data presented enable the estimation of any two of the above three variables, if the third variable is known. The authors wish to thank Miss Huei-Kuen Ying and Mrs. Anne F. Rogers for their technical assistance, and Mrs. Rhoda C. Sparrow and Mrs J. Van't Hof for aid in preparing the manuscript. * Research carried out at Brookhaven National Laboratory under the auspices of the U.S. Atomic Energy Commission.

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Three approaches to the simultaneous sedimentation and diffusion of hands or zones of noninteracting homogeneous macromolecules are examined: (1) The authors' method of moments: (2) the transport me of Sehumaker and Rosenbloom; and (3) the stochastic solution of the Lamm equation due to Gehatia and Katehalski. All three methods indicate that the motion of the maximum of the hand may be used to evaluate the sedimentation coefficient. The moment, method provides relations which appear to be useful for measuring diffusion coefficients. Relations are given for the analysis of resolved components. The problem of measuring sedimentation coefficients of macromolecules with concentration‐dependent sedimentation coefficients is examined. Methods are described for evaluating the sedimentation coefficient in these systems and for obtaining the sedimentation coefficient at infinite dilution. Methods are described for determining the weight‐average sedimentation coefficient in Multi‐component systems, and the differential and integral distribution of sedimentation coefficients of macromolecules with low‐diffusion coefficients.

When T-even phage infect Escherichia coli, synthesis of host deoxyribonucleic acid (DNA) rapidly ceases. If the phage carry a mutation in a gene essential for phage DNA synthesis, then the infected bacteria should make no DNA, either host DNA or phage DNA. However, we have found that infection with certain T4 gene 56 (deoxycytidine triphosphatase)-rII double mutants leads to substantial DNA synthesis. Only rII deletion mutations which extend into the middle third of the adjacent, nonessential D region lead to the anomalous DNA synthesis, when combined with a gene 56 mutation; the requirement probably is that the deletion extend into the D2a transcriptional unit identified by Sederoff et al. Genetic evidence indicates that the observed anomalous DNA synthesis is synthesis of phage DNA. We suggest that the D2a region controls, directly or indirectly, a nuclease involved in the breakdown of cytosine-containing DNA. In the absence of the D2a product, the cytosine-containing phage DNA made by the gene 56 mutant is stabilized.

SynopsisThree types of band-forming centerpieces nseflil in h i t 1 ccnt,rifllgation in the anttlyt,i-The mode of filling arid the :tdvant,zges and disadcal iiltracentrifuge are described. vantages of each type are discussed.