1911] GATES—CHROMOSOME REDUCTION 335 
nucleus in fig. 4, and it is equally evident that the threadwork in 
the synaptic ball is much denser than that in the reticulum of 
fig. 4. Undoubtedly the most important thing that is going on 
at this time is a rearrangement of the threads of the reticulum to 
form the more or less continuous threadwork of synapsis. But 
similar rearrangements go on in the prophase of every somatic 
mitosis. The peculiar appearance is given to synapsis, and in 
some degree to the subsequent stages up to diakinesis, by the 
enormous growth of the nuclear cavity; but, as already pointed out, 
there is also a certain amount of contraction as the threads of the 
reticulum become transformed into those of the synaptic ball. 
In the paper cited I interpreted synapsis in the ordinary way, 
as resulting from a contraction, but it is evident that this only 
partly explains the phenomenon, which is largely due to an increase 
of the karyolymph, accompanied by a rearrangement, without 
any growth, of the chromatic threads.® It is to be hoped that 
future students of reduction will make careful series of measure- 
ments, to see whether the same size relationships hold for other 
forms. In making such measurements it will be necessary to take 
account of the fact that in the later stages of synapsis the nuclear 
membrane frequently becomes extremely delicate or practically 
disappears, allowing the cytoplasm to encroach on the nuclear 
SIna conversation with Dr. Lawson at Brussels during the Botanical Congress, 
he first suggested to me that the synaptic appearance is due to a growth of the nucleus 
rather than a contraction of the nuclear contents. He has since kindly sent me an 
advance proof of his paper (12a), the appearance of which was unfortunately delayed, 
So that I might make more extended reference to it. In studies of the pollen mother 
cells of Smilacina at the time of synapsis 
in the cytoplasm. Our results, therefore, are essentially in agreement. LAwsoNn 
attributes the growth of the nucleus in the pollen mother cell to the fact that the latte 
18 charged with food materials, which leads to the disappearance of vacuoles from the 
plasm, and an accumulation of sap within the nuclear cavity. The fact that 
“ynapsis is now known to be almost coextensive with sexuality itself, occurring even 
in Myxomycetes (OLIvE), would seem to call for a more general explanation of the 
Phenomenon. Later in the present paper I have suggested the direction in which 
it seems probable to the writer that the explanation of the nuclear growth without 
chromatin growth, which causes the synaptic appearance, is to be found. 
