RECIPROCAL TRANSLOCATION 335 



For example, (E. Hookeri had seven normal bivalents, CE. franciscana 

 a ring of four and five bivalent pairs, ffi. ruhrinervis a ring of six and four 

 pairs, CE. ruhricalyx a ring of eight and three pairs, OE. biennis (from 

 Munich) a ring of eight and a ring of six, (E. strigosa X Lamarckiana 

 cruciata a ring of ten and two pairs, CE. Lamarckiana a ring of 12 and one 

 pair, and CE. muricata a ring of 14 with no free pairs. Genetical investiga- 

 tions showed that the more chromosomes there are in the ring or chain, the 

 larger the number of linked genes (Cleland and Oehlkers). Of special 

 importance were the discovery by Cleland of the fact that alternate 



(gJ (Le+hal)(6/5 j 



^ — / V_y Loim. ( GV 



X 



? 



V ) (Le+ho.l)( V, 



Fig. 192. — The cytogenetic composition of (Enothera Lamarckiana. A, distribution of 

 the Renner complexes gaudens (G) and velans (F) in reproduction. Only the heterozygotes 

 survive. B, the chromosomes at diakinesis. Those carrying the gaudens and velans 

 complexes are marked G and F, respectively. Interchanged chromosomes indicated by 

 transverse marks. (Based on data of Renner, Cleland, and Blakeslee.) 



chromosomes in the ring as a rule pass to the same pole in anaphase / 

 (Fig. 191) and his suggestion that each chromosome has a constant posi- 

 tion in the ring.*^ This results in the formation of spores and gametes 

 with only two assortments of chromosomes, so far as those in the ring are 

 concerned. Since certain chromosomes thus tend to remain together, 

 they function like a single large chromosome as carriers of linked genes. 

 As soon as the theory of reciprocal translocation had been formulated, 

 it was evident to those^ who employed it in their investigations that here 

 was probably one of the principal keys to the CEnothera problem. Its 



For lists of chromosome configurations in the various species, see Cleland (1925), 

 Cleland and Oehlkers (1929, 1930), and Illick {19326). 



^ It has since been shown directly in Rhoeo that the 12 chromosomes in the ring do 

 have constant positions (Sax, 1931e), and furthermore that the direction in which 

 the chromonemata coil tends to be constant for the given distinguishable members 

 (Nebel, 19326). 



^ Belling, Sturtevant, S. H. Emerson, Meurman. The first discussions of the 

 question in the literature were those of Hakansson (1928a) and Darlington (1929a, 

 1931e). That CEnothera Lamarckiana combines unlike chromosome sets was suggested 

 by Lotsy (1917, 1919). 



