Band 141. Nr. 15. XL. Jahrgang. IL Bd. Nr. 15. 



Botanisches Centralblatt. 



Referierendes Organ 



der 



Association Internationale des Botanistes 

 für das Gesamtgebiet der Botanik. 



Herausgegeben unter der Leitung 

 des Präsidenten: des Vice- Präsidenten: des Secretärs: 



Dr D H. Scott. Prof. Dr. Wm. Trelease. Dr. J. P. Lotsy. 



und der Redactions-Commissions- Mitglieder: 



Prof. Dr. Wm. Trelease, Dr. C. Bonaventura, A. D. Cotton, 



Prof. Dr. G. Wehmer und Mag. G. Christensen. 



von zahlreichen Specialredacteuren in den verschiedenen Ländern. 



Dr J. P. Lotsy, Chefredacteur. 



Abonnement für das halbe Jahr 25 Mark 

 Wo. 40. durch alle Buchhandlungen und Postanstalten. 



1919. 



1 Alle für die Redaction bestimmten Sendungen sind zu richten an: , 

 Redaction des Botanischen Centralblattes, Haarlem (Holland), Spaarnei7. 



Bridges, C. B., An intrinsic difficulty for the variable 

 force hypothesis of crossing over. (Amer. Naturalist. LI. 

 p. 370-373. 1917.) 

 The hypothesis of a „variable specific force", assumed by 

 Goldschmidt may seem to account for the frequency of the 

 crossovers occurring in a simple case of linkage, but the writer 

 shows in this present paper, that this explanation when extended 

 to the results which such crossovers give when bred, it creates a 

 difficulty of the same type and magnitude as the original problem 

 of crossing over, for which, therefore it is not a satisfactory Solution. 

 Goldschmidt's hypothesis includes the necessity of comple- 

 mentary coupling-intensities when a heterozygote results by a 

 cross-over-mating and when this heterozygote gives again cross-over 

 gametes. As everyone acquainted with linkage knows, says the 

 writer, the cross-overs given by the heterozygote from the mating 

 of two cross-overs are of the same frequency as in the original 

 experiment. The intensities of coupling and repulsion are equal and 

 not complementary. The whole explanation of Goldschmidt fails 

 onless some added agency be devised to take over the duty which 

 the specific allelomorphic forces abandon after the occurrence of 

 crossing over. An interchange of forces must be subsequent to the 

 interchange of the genes. These reciprocal transformations of the 

 forces cannot be explained by Goldschmidts hypothesis, and if 

 it could, we could have sidetracked this whole machinery by 

 applying this reciprocal transmutation idea to the genes and thereby 

 have solved the original problem. M. J. Sirks (Wageningen). 



Bwtan. Centralblatt. Band 141. 1919. 15 



