910 Gates.—Pollen Formation in Oenothera gig as. 
number of chromosomes there is a corresponding increase in the nuclear 
volume. As is well known, Nemec (’ 10 ) has obtained similar results in his 
experimental production of chromosome doubling in root-tips. 
It does not necessarily follow, however, that a variety with larger cells 
will have the tetraploid number of chromosomes. This is shown by the 
case of a giant race of Primula sinensis , in which Gregory (’ 09 ) found that, 
though the cells were larger, the chromosome number was unchanged. 
There are therefore two types of giantism in plants, one in which the 
tetraploid chromosome number is accompanied by a doubling in the nuclear 
volume and an accompanying increase, in varying proportions, in the volume 
of the cells ; another, in which the amount of chromatin has not appreciably 
changed, while the cytoplasm has undergone a large increase. In the latter 
case there must be a marked change in the karyoplasmic relation, while in 
the former there is no change in the karyoplasmic ratio or, as my measure¬ 
ments show, a relatively small change. 
A further consideration of the size relationships between O. gigas and 
O. Lamarckiana will not, however, be entered into in the present paper, 
the purpose of which is to give an account of the pollen formation in 
O. gigas. The process of chromosome reduction in Oenothera has already 
been described by me in some detail in several previous papers, including 
a study of O. Lamarckiana and several of its mutants, notably O. rubri - 
nervis (’ 08 ) and O. lata , and the hybrid O. lata x O. gigas (’09 b) ; as well as 
a study of O. biennis and O. laevifolia (’09 c) ) in both of which the phenomena 
of reduction were found to be precisely the same as in O. Lamarckiana or 
O. rubrinervis. 
Since diakinesis and certain other stages of the reduction process were 
studied with special care in a previous paper (’ 08 ), in which the method 
of chromosome pairing and the main events in the history of the chromo¬ 
somes during meiosis were, I think, satisfactorily demonstrated, the present 
paper will not attempt to give another complete series showing all the 
events of meiosis, but attention will be concentrated upon certain stages 
which have been intensively studied. Of these, the series of stages or 
conditions which are usually grouped together under the term synapsis has 
received much attention, with the result that more changes in the nucleus 
are found to occur during this period than has previously been supposed. 
A type of pollen sterility which differs in certain respects from any previously 
known in plants will also be described, and certain variations in the 
phenomena of meiosis will be considered. 
The material for these studies was all obtained from plants of O. gigas 
grown in connexion with my pedigree cultures, and which were derived 
originally through the kindness of Professor de Vries, from seeds descended 
through several generations from an original single mutant in his garden at 
Amsterdam. 
