Sunshine Conditions Research Articles

Ice-Worms in Yukon and Alaska

I FOUND a considerable number of the oligochaetous annelids known as 'ice-worms' on August 7, 1949, during the Arctic Institute's Project Snow Cornice in the St. Elias Range, Yukon–Alaska Boundary. They were discovered on the Seward firnfield at an altitude of about 6,000 ft., and scattered sparsely over the surface of the neve at midday in conditions of bright sunshine. They were mostly ¾inch or less in length and black in colour' but under the hand-lens appeared brownish-black, when fresh, and before preservation in 'B.C. Fix' (alcohol + acetic acid + formalin). They quickly dried up and died at ordinary air temperature when taken from the snow or melt-water.

A FERTILE TRIPLE HYBRID, NICOTIANA TABACUM × (NICOTIANA SYLVESTRIS ×NICOTIANA RUSBYI). PRELIMINARY REPORT

The hybrids obtained after crossing N. Tabacum (n = 24) X N. sylvestris (n = I2), N. Tabacum (n = 24) X N. Rusbyi (n = I2), N. sylvestris (n = 12) X N. Rusbyi (n = I2), and from the reciprocal crosses are self-sterile under normal conditions. The cytological studies on these three species hybrids (Kostoff, I930) showed that in the pollen mother cells (PMC's) of the first two there were 12 bivalent and 12 univalent chromosomes appearing during the first meiotic division, while in the hybrid of the third cross, N. sylvestris X N. Rusbyi, 24 univalent chromosomes were usually found. The latter cross combination formed occasional dyads with 2n, i.e. 24, chromosomes instead of tetrads as a result of omission of the first meiotic division. This occurred most frequently when the hybrid plants from this cross grew under conditions of insufficient water supply and intense sunshine. When N. Tabacum was pollinated with pollen from the hybrid N. sylvestris X N. Rusbyi containing a relatively high percentage of pollen grains originating from such dyads, seeds were obtained from which very vigorous plants-triple hybrids, N. Tabacum X (N. sylvestris X N. Rusbyi)-were raised (P1. X, figs. I and 2). Among these triple hybrid plants intermediate types were found as well as those that resembled more closely one of the parental plants in respect to certain characters. The intermediate types (figs. I, 2, and 3) proved to be fully fertile while the others were only partially so. Cytological studies on both types of plants were made and it was found that the partially fertile plants had a relatively irregular reduction division and usually 48 + i, or 48 + 2 somatic chromosomes, while the fertile intermediate triple hybrids had normal, regular, reduction division (figs. 4 and 5), and had 24 chromosomes in the PMC's (fig. 4) and 48 in the root tips (figs. 6 and 7). The origin of these fully fertile triple hybrids can be explained on a cytological basis as follows: As manifested by the F1, half of the chromosomes of N. Tabacum (n = 24) have an affinity for the chromosomes of N. sylvestris (n = 12) and the other half (I2) have an affinity for those of N. Rusbyi, while the chromosomes of N. sylvestris do not manifest any such affinity for the chromosomes of N. Rusbyi as also observed in the F1 plants. However, after pollinating N. Tabacum with pollen from F1 (N. sylvestris X N. Rusbyi) which contained a high percentage of abortive grains and also those originating from dyads with 24 chromosomes (12 from N. sylvestris and I2 from N. Rusbyi conse-

On English Lagoons

YET another book about the Norfolk Broads, or, as the author prefers to call them, the “English Lagoons.” One can hardly credit that anything fresh could be said on this well-worn subject, but Mr. Emerson's book differs from all that have gone before in being a continuous narrative of a twelve months' sojourn on the Broads in his pleasure wherry, the Maid of the Mist, and presents to us a graphic picture of these waters under their winter aspect as well as under a summer sky. Much that he has written, more particularly his excellent descriptions of the peculiar scenery of this remarkable admixture of land and water in mid-winter, is highly interesting. The atmospheric effects under various conditions of storm and sunshine, by moonlight and at early dawn, display a keen artistic perception, but the incidents as a rule are trivial in the extreme in fact, and the constant use of the vernacular becomes tiring—whole chapters (e.g. Chapter xxi. of six pages) might have been well omitted. On English Lagoons. By P. H. Emerson. (London: David Nutt, 1893.)