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in the older literature are to be expected, for at the time, the steps in mitosis were not so specifically defined. In this description, reference is made to the individual chromosome and not to tetrads as such.My material was prepared by the modernized aceto-carmine method as described by Belling (I92Ib). Material was also fixed in Flemming's medium fluid followed by sectioning and staining. In addition to these methods, pollen mother cells were teased out on a slide into a 3 percent cane-sugar solution and studied in the living condition. The staminate hairs were suspended in 3 percent cane sugar, and the course of the divisions could be followed as described by Strasburger (Practicum, p. 604) for the staminate hairs of Tradescantia and by Lundegardh (I9I2b) for root-tip divisions. The temperature was satisfactory when between 75°and 80°F.The drawings of Plate XXIX were made entirely from aceto-carmine preparations. This is certainly a most valuable reagent for studying the chromatic elements of a cell to the exclusion of others. The solution may be employed in any dilution, and I found that for general purposes one drop of the modernized Schweigger-Seidel (1868) preparation added to one drop of water on a slide gave almost instantaneous staining.The fluid acts as a swelling agent, so that the preparations in a one-toone dilution go to pieces in about a week. For this reason, it is desirable to know how soon after treatment the chromosomes will show any particular stage in the swelling.The mother cells were teased from the anthers into a drop of water on a slide to which then was added, ordinarily, a drop of the aceto-carmine. The mount was made as described by Belling (1921bj, who first instructed me in the method. It was noted, in cases in which the stain was run under the cover glass, that about ten seconds were required to bring the chromosomes into the sharpest definition.The structure came out with the first swelling, somewhat as does the image on a photographic plate, without any perceptible change either in the form or in the position of the elements from that seen in the living condition. The first perceptible change can be noticed in about an hour, when the elements mayor may not appear a trifle swollen. When slight swelling' occurs, it affords considerable advantage for studying the morphological composition of the chromosomes.The figures given on the accompanying plates were, for the most part, made shortly after fixation, i.e., after some slight swelling had occurred.

A micro dissection of the pachytene threads of Tradescantia virginica L. shows that the relation of the chromosomes is a matter of continuous linkage in a chain and that, undoubtedly, division and segregation are everywhere processes of abstriction with subsequent mechanical distribution of the elements.

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