The Ohio ^JSCaturalist, 



PUBLISHED BY 



The Biologkal Club of the Ohio State Uni-versity, 

 Volume XIV. NOVEMBER, 1913. No. 1. 



TABLE OF CONTENTS. 



McAvoY— The Reduction Division in the Microsporocytes of Oenothera Biennis 189 



SCHAFFNER— The Classification of Plantt^, X 198 



Britten and Brown's Illustrdted Flora 203 



THE REDUCTION DIVISION IN THE MICROSPOROCYTES 

 OF OENOTHERA BIENNIS.* 



Blanche McAvoy. 



While making a study of the reduction division in Fuchsia (8) 

 it became necessary to review the Hterature on the Oenotheras. 

 Finding that Geertz (7), Gates (3, 4, 5 and 6), and Davis (1 and 2), 

 did not entirely agree among themselves and finding also that my 

 study of Fuchsia (8) did not agree in all respects with that of any 

 of the investigations on the evening primrose, I also became 

 interested in the problem presented by the reduction division 

 of Oenothera. 



Geertz (7) describes the threads occurring in the early stages 

 of Oenothera lamarckiana as being irregular in thickness and 

 containing small discs of chromatin. He calls the contraction 

 stage synapsis and speaks of loops extending out from the con- 

 tracted knot. He says the fully formed chromosomes are found 

 immediately after the contraction and that the bivalent chromo- 

 somes are produced by a pairing of univalent chromosomes, but 

 he does not find a conjugation of two threads during the contrac- 

 tion. He also observes a longitudinal splitting of the chromosomes 

 just after the transverse split occurs. 



Gates has made various studies of the Oenotheras namely 

 O. rubrinervis (4), O. lata xO. gigas (6), O. lata xO. lamarckiana 

 (3), and 0. gigas (5). In his paper on O. rubrinervis (4) he 

 insists that the contraction stage is not an artifact but a natural 

 stage leading to synapsis. After the contraction the chromatin 

 material arranges itself in threads which shorten, contract and 

 finally constrict so as to show fourteen univalent chromosomes. 

 These break apart in pairs, each pair fusing together to form a 

 bivalent chromosome. His second paper (6) is a study of the 

 continuity of chromosomes. He claims that there are two methods 



* Contribution from the Botanical Laboratory of Ohio State Univer- 

 sity, No. 76. 



