'The Ohio Naturalist, 
PUBLISHED BY 
The Biological Club of the Ohio State University. 
Volume XIV. NOVEMBER, 1913. 
No. 1. 
TABLE OF CONTENTS. 
McAvoy —The Reduction Division iu the Microsporocytes of Oenothera Bienuis. 189 
Schaffner— The Classification of Plants, X.. . 198 
Britton and Brown’s Illustrated Flora. 203 
THE REDUCTION DIVISION IN THE MICROSPOROCYTES 
OF OENOTHERA BIENNIS.* 
Blanche McAvoy. 
While making a study of the reduction division in Fuchsia (S) 
it became necessary to review the literature 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 
0. rubrinervis (4), O. lata xO. gigas (6), O. lata xO. lamarckiana 
(3), and O. 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. 
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