No. 3, July, 1921] GENETICS 277 



alveolata (annelid), larvae were also exclusively maternal. Author concludes that true hy- 

 brids are not produced among moUusks. Even closely related and ill-defined species usually 

 produce false hybrids exhibiting maternal characters, and only exceptionally are individuals 

 found which appear to be true hybrids. — R. E. Clausen. 



1935. Plough, Harold H. Further studies on the effect of temperature on crossing over. 

 Jour. Exp. Zool. 32: 197-202. 3 fig. 1921. — Since preliminary work on the 1st and 3rd chromo- 

 somes of Drosophila nielanogaster had indicated that crossing over was not visibly affected by 

 temperature changes, the author undertook experiments to determine why these chromosomes 

 differed from the 2nd where a temperature above or below the optimum causes a significant 

 increase in crossing over. The tests were made at a temperature of 31.5°C., and the crosses 

 were between wild stock and mutant stocks of the 1st and 3rd chromosomes. The controls 

 were kept at a temperature of 22-25°C. The Fi were back-crossed to the original mutant 

 stocks and the per cents of crossovers calculated. Practically the whole length of these 2 

 chromosomes was tested in this way. The experiments with the 1st chromosome showed that 

 crossing over in this chromosome is not influenced by temperature or by the age of the female 

 parent. The results with the 3rd chromosome were somewhat different. There was an 

 increase in crossing over in this chromosome due to temperature, in only one region — the 

 sepia-spineless. A variation in crossing over with the age of the female occurred also in this 

 part of the chromosome only. Other regions of the chromosome were unaffected by tempera- 

 ture or age of the female parent. This same section, only, showed a relatively high rate of 

 double crossovers. A similar phenomenon had been found to occur in the 2nd chromosome, 

 where the region which showed high rate of double crossing over was influenced in the amount 

 of crossing over by temperature or age of the female parent. The author interprets these 

 results as indicating that regions where crossing over occurs less freely are the ones which 

 are "sensitive" to the effects of environment. — Mildred Hoge Richards. 



1936. Rawson, H. E. Plant-sports produced at will. Proc. Linn. Soc. London 1919: 

 64-65. 1920. — Through "selective screening" experiments on various plants, such as Tro- 

 paeolum majus and Papaver Rhoeas, author claims to have secured sports and new varieties. 

 By "selective screening," the author refers to a system of screening plants at selected inter- 

 vals of daylight. Variations produced by this method are said eventually to have become 

 hereditary or '"fixed," that is, they appeared without "selective screening" in the open garden. 

 A double variety of poppy is believed to have originated in this way. Sudden changes of 

 color or structure were accompanied by sterility. "Selective screening" brings out latent 

 potentialities and causes correlated variations. Work of Garner and Allard [See Bot. 

 Absts. 5, Entry 22] is said to support these views. — Orland E. White. 



1937. RiCHET, Charles, et Henry Cardot. La transmission hereditaire des caracteres 

 acquis et I'accountumance des microbes. [The hereditary transmission of acquired characters 

 and the behavior of microorganisms.] Compt. Rend. Acad. Sci. Paris 171 : 1353-1358. 1920. — 

 A study of the resistance of lactic-acid bacteria to various chemical substances. A resistance 

 was noted for potassium bromide, saccharose, vanadium, zinc, copper, and phenol; but the 

 organisms became more and more sensitive to mercuric chloride. A specific resistance was 

 developed in successive generations with respect to thalliiun nitrate, but this race was not 

 resistant to other toxic substances. The development of resistance seems not to be a gradual 

 process, but seems to occur suddenly in the manner of a mutation. These results seem to in- 

 dicate that in the use of antiseptics, the same one should not be used continuously, but the 

 different types should be alternated. — Mrs. W . K. Farr. 



1938. RiTZMAN, E. G. Breeding earless sheep. Jour. Heredity 11: 238-240. Fig. SI. 

 1920. — An account of the production of an earless type of sheep, at the New Hampshire Agri- 

 cultural Experiment Station, by crossing 2 ?hort-eared types. The short ears ranged below 

 2f inches in length and were formerly (Jour. Agric. Res. 6: 1916) reported to be the somatic 

 expression of the pure dominant and of the heterozygote, assuming complete dominance. 

 The later results reported show that the pure dominant is somatically earless and that the 



