2 BOTANICAL GAZETTE [JULY 
The cytological studies presented here will be confined chiefly to 
the phenomena of synapsis and reduction in the pollen mother cell. 
Various forms have been studied, a complete series of stages being 
obtained in some forms and a partial series or only a few stages being 
examined in others. The forms investigated include (1) O. rubri- 
nervis, (2) O. Lamarckiana, (3) O. gigas, (4) O. nanella, (5) O. biennis 
cructata, a variety of the European O. biennis, (6) both O. lata (see 12) 
and O. Lamarckiana from the F , of O. lata O. Lamarckiana, and (7) 
plants resembling O. gigas, from the F, of O. lataXO. gigas. Pre- 
liminary reports have already been made upon some of these studies, 
in various connections (II, 12, 13, 14, 15). Reference will be made 
to some of these results later. 
The material from each individual was collected separately in 
nearly all cases, in order to observe possible individual differences in 
the same race, either in the number of chromosomes or in other 
cytological features. I am indebted to Mr. C. H. SHarruck for 
making a number of these collections. The material for the study of 
O. rubrinervis was obtained from a number of individuals grown in 
two different seasons and representing several strains derived from the 
same original pedigree. Sections were cut from six of these, and it 
may be stated here that in O. rubrinervis no individual differences 
were discovered, either in the number of chromosomes, which was 
14 in all cases, or in any other features. In some of the other mutants, 
also, a number of individuals were examined. It was found necessary 
to reserve the account of O. gigas, which presents several features of 
special interest, for a separate paper. A preliminary report on this 
form has already been made (14, 15). 
For various reasons, O. rubrinervis was chosen as the most favor- 
able form for a thorough study of synapsis and reduction. The 
nuclei and chromosomes of Oenothera are small, and for this reason 
the selection of the most favorable type for study is a matter of some 
importance. In O. rubrinervis the pollen mother cells, although 
they vary much in size, are usually considerably larger than in 
O. Lamarckiana, the nuclei being also proportionately larger. The 
reason for this will be explained later. The chromosome number 
being low in most of the forms (2% =14, «=7), they can be counted 
without any difficulty, notwithstanding their small size. Another 
