Haploids in Hordeum Vulgare.

suns. The extension of the Andromeda nebula beyond the photographic limits is presumably typical of what may be found for other such objects. Comparisons with the surface brightness of the galaxy are still hampered by uncertainties in the data for our own system. There may be no part of the galaxy which, seen from outside, would be as bright as the central portion of M 31. In the latter system the region comparable with the sun's neighborhood may well be 10 out from the nucleus, or at a distance of say 4000 parsecs, where, according to the data shown on plate 1, the surface brightness agrees fairly well with Seares's previously mentioned estimate fot our own system. A previous suggestion4 gave 30,000 parsecs for the diameter of the galaxy, with the sun 10,000 parsecs from the center, as against 10,000 parsecs for the diameter of the nebula. The present work indicates that the diameter of the nebula may well be as much as 20,000 parsecs. The figure for the galaxy may have to be revised still further when the space absorption near the median plane is better determined. In fact, when the size of our galaxy is as well known as that of the Andromeda nebula, most of the inferred difference in scale between the two systems may disappear. The construction of the amplifier at Madison and its use at Mount Wilson were made possible by grants from the National Research Council and from the California Institute of Technology, the latter in connection with plans for the 200-inch reflector. * NATIONAL RESEARCH FELLOW. 1 Mt. Wilson Contr., No. 191, p. 12; Astrophys. J., Chicago, Ill., 52,162-182, 177 (1920). 2 Ibid., p. 5. 3 Mt. Wilson Contr., No. 453, p. 11; Astrophys. J., 76, 106-116 (1932). 4 Stebbins, J., these PROCEEDINGS, 19, 227 (1933).