No. 4, January, 1921] GENETICS 247 



16S7. IIakmw, M ary T. Chromosome studies in Tettigidae. II. Chromosomes of BB, 

 CC, and the hybrid BC in the genus Paratettix. Anal. Etec. 17: 329. Jan., 1920.— Auth 

 abstract of paper read before t lit- American Society of Zoologists, St. Loui . December 30, 

 Pip.i. BB, C( !, and their hybrids, B< ' I N *.boi rb, I'M l and L917), are the only forms considered 

 in this paper. Six pairs and an unpaired chromosome are present in th rria. 



In BB tip- chromosomes of the third pair, according to size, taper toward i end and are 



bent so as to have almost the appearance of a hook. In CC the chi les of this pair 



are nearly oval. In the li\ brid, B< 5, this pair of chromosomes is composed of an oval chromo- 



e like that in CC and a bent chromosome like thai in BB. The difference in this homol- 

 ogous pair of chromosomes is recognized at the end of the growth period previous to the 

 formal ion of the chromosomes of the first maturat ion spindle.— The diploid number of chromo- 

 somes appears at the end of the growth period previous to the formation of the bivalent 

 chromosomes. The bivalent chromosomes are formed by an end-to-end union of the homol- 

 ogous pairs of these chromosomes before they have been completely condensed. The 

 chromosome may be recognized at all stages.— In the first maturation division the bivalent 

 chromosomes separate at the line of union, and the sex chromosome goes to one pole undivided. 

 The formation of the diploid number of chromosomes at the end of the growth period and the 

 union, end to end, of their homologous pairs may explain the absence of any crossing-over in 

 Paratettix— -Mary T. Harman. 



1688. Haetwell, Burt L. Thirty-second annual report of the Director of the Rhode 

 Island Agricultural Experiment Station. Bull. Rhode Island State Coll. 15:69-84. Feb., 

 1920. — Brief statement on pages 82, 83, of inheritance studies with poultry and rabbits.— 

 G. II. Shull. 



1689. IIeribert-Nilsson, Nils. Zuwachsgeschwindigkeit der Pollenschlauche und 

 gestorte Mendelzahlen bei Oenothera Lamarckiana. [Decline in pollen-tube growth and 

 deranged Mendelian ratios in Oenothera Lamarckiana.] Hereditas 1:41-67. 1 fig. 1920. — 

 Author has investigated the rate of growth of pollen tubes by cutting off the base of the 

 style at certain intervals of time after pollination. Temperature influences considerably the 

 velocity of growth of the pollen-tubes. — Rr (red-nerved) X rr (white-nerved) give the typical 

 Mendelian segregation 1:1. The inverse cross (rr X Rr) gives too large proportion of red- 

 nerved plants. The R tubes grow more rapidly than the r tubes, and consequently fertilize a 

 number of eggs before the r tubes arrive, in 1918 segregations up to 4: 1 were obtained. 

 Competition between R and r is termed certation, and the cross rr X Rr a certation-cross. 

 The inverse cross is called an equation-cross. Difference in the influence of temperature be- 

 tween the R and r tubes is to be interpreted in such a way as to explain the slow growth of the 

 r tubes becoming relatively still more retarded when the temperature falls. — By self-fertili- 

 zation of Rr plants we meet besides certation other complications. All the red-nerved plants 

 are heterozygous, Rr. The combination RR can not be produced. Consequently a segre- 

 gation in the ratio 2 Rr: 1 rr is to be expected. However, the author obtained too many Rr 

 plants. No elimination of RR zygotes takes place, but there is a repulsion between the R 

 gametes, a "prohibition." All the R eggs are fertilized by r pollen. The compensation of 

 the R pollen with r pollen in the fertilization of the R eggs receives the name "substitution." 

 Thus the ratio 2 Rr -f 1 rR to 1 rr is obtained; that is, the segregation 3: 1. By cooperation 

 of certation the segregation is found to be 6: 1 in extreme cases. The irregular segregation 

 stated by de Vries can be explained by the complications characteristic of the factor R. 

 The more Oenothera Lamarckiana is examined, the more the variability proves itself not to 

 be a phenomenon sui generis. — K. V. Ossian Dahlgren. 



1690. Heribert-Nilsson, N. [German rev. of: von Hofsten, N. Arftlichetslara. 

 [Genetics.] 17 X 26 cm., viii + 506 p., 191 fig., 1 colored pi. P. A. Norstedt & Soners forlag: 

 Stockholm. 1919. (See Bot. Absts. 3, Entry 2208.)] Zeitschr. indukt. Abstamm. Vererb. 

 24:98. Aug., 1920. 



