1. The material used in this investigation is the pollen mother cells of Linum perenne, L. which were fixed in BOUIN'S solution. Sections were cut at seven micra and stained with iron-alum-haematoxylin. 2. As shown in Figs. 3 and 4, the pairing spireme of the diplotene stage divides into four sections with a slender neck in the middle of the threads. Probably this is the origin of the tetrad chromosomes. Towards the end of the diplotene stage the spireme gradually contracts developing into the more compact gemini of the following diakinesis. Consequently in the, early shorty afterward, by the end of the dickinesis, the tedrad chromosomes becomc more contracted diakinesis, as shown in Figs. 5 and 6, the slender part of the spireme (gemini) becomes some-what obscured. But in the late diakinesis when the pairing gemini have contracted further and become more or less roand, there appears a narrow crack in the middle part of each of the pair dividing them into four sections (Fig. 7 a). These four are the tetrad chromosomes. But shortly afterward, by the end of the dickinesis, the tetrad chromosomes become more contracted and form the double chromosomes of the first metaphase (Figs. 7 a and 9). 3. Sometimes during the late diakinesis ring shaped chromosomes are formed by the joining of the pairing gemini at the ends (Fig. 8 a). Though the formation of these fings is sometimes very obscure, it is probable that they are the tetrad chromosomes. After continued contraction these rings gradually change into the double chromosomes of the first metaphase (Figs. 8b and 9). 4. In view of the arrangement of the pairing spireme in the diplotene stage (Figs. 2, 3, and 4), it appears that in Linum perenne we have an instance of parasynapis which is so rare in plant cytology that it invites further study.
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