912 
Gates.—Pollen Formation in Oenothtra gigas. 
A series of measurements of the pollen mother-cells and nuclei of 
0 . gigas further confirms this view, and shows that while there is some 
growth of the pollen mother-cells during the period between the beginning 
and the completion of nuclear c contraction yet this is not in proportion to 
the very large increase in the size of the nucleus during this period. This 
result is in general agreement with Lawson’s (’ll) interpretation of synapsis 
from his study of Smilacina. The results of these measurements will not 
be presented in detail in the present connexion, but they show that, between 
the resting telophase of the last archesporial division and the synapsis 
(synizesis) condition, the pollen mother-cells and their nuclei undergo 
a simultaneous growth for a considerable period, during which a very large 
amount of increase in size takes place. In an earlier paper (Gates, ’ 08 ) 
the same was shown to be true of the forms with fourteen chromosomes. 
This is followed by a rather sudden expansion of the nucleus at the 
beginning of ‘ synapsisThe mother-cell having nearly completed its 
growth just before the beginning of the phenomenon of synapsis, its subse¬ 
quent enlargement is relatively small, so that the ratio — ^^ .- V °^ ume - 
nuclear volume 
is conspicuously greater just before synapsis than in cells in the synaptic 
condition. This is clearly shown by a comparison of Figs, i and 5, PL 
LXVII. In Fig. 1, however, the nucleus is a trifle smaller than the average 
size at this time. Certain conclusions in connexion with this interpretation 
of synapsis have been discussed in another paper (Gates, ’ll) and need not 
be referred to here. A number of other features of exceptional interest 
have since developed in connexion with further study of synapsis, and 
these will be discussed in the present paper. 
It is of course necessary to determine what pollen mother-cells are 
about to enter upon synapsis. One finds that in certain anthers of flowers 
at about this stage, some of the pollen mother-cells will be in the condition 
shown in Fig. 2, in which the synaptic process is just beginning. In such 
anthers other mother-cells do not show such ‘clear spaces’ adjoining their 
nuclear membrane, and such nuclei can safely be taken to be in the stage 
just preceding the beginning of synapsis. 
There appears to be wide variation in the manner in which the nuclear 
expansion which produces the ‘ synaptic ’ condition comes about. In some 
cases (Fig. 2) its early stages are certainly very gradual, there being an 
expansion of the nuclear membrane which sets it free from the nuclear 
reticulum, leaving clear areas at one side of the nucleus, occupied only by 
karyolymph. Expansion of the nuclear membrane in this manner may 
continue until the nucleus has attained to nearly its definitive size. This 
may have been the case in the nucleus represented by Fig. 5. Sooner or 
later, however, in this growth period of the nucleus, the nuclear membrane 
is likely to become very delicate and indistinct, or it may break down 
