THE QUESTION OF POST-REDUCTION IN SPHAGNUM

The 19 spatially distinct chromosomal units at first meiotic metaphase in sporophytically diploid species of Sphagnum have usually been considered to be bivalents, but one investigator (Sorsa, 1956) has interpreted them as chromosomes from dissociated bivalents and meiosis as post-reductional. The present studies on diploid S. squarrosum (Pers.) Crome establish the chromosome number on the basis of the following evidence: there are in addition to m-chromosomes, 19 pairs of chromosomes in early prophase, 19 bivalents at diakinesis, 19 chromosomes in each of the two sets at second metaphase, 19 daughter chromosomes in each of the four sets at late second anaphase, and 19 chromosomes in gametophytic mitoses. The 19 bodies at first meiotic metaphase in diploid species are true bivalents in loose secondary association, which has led to their erroneous interpretation as chromosomes of dissociated bivalents. The gametic chromosome number in sporophytically diploid Sphagnum is therefore, without doubt, n = 19, and this evidence negates the claim for post-reduction in Sphagnum.     

ON THE QUESTION OF LONG-LIVED RNA IN MAMMALS

RNA was isolated from various mouse tissues 126 days after the injection of ¹⁴C-uridine and 37 days after the injection of ³H-uridine. Calculations based on a small but definite residual amount of ¹⁴C-labeled RNA suggest the existence of an RNA with a half-life in excess of 10 days. Independent calculations based on the ratio of ³H and ¹⁴C dpm in chromatographically isolated UMP suggest a minimum half-life of about 30 days.