Acer negundo , L., and Staphylea trifolia , Z. 117 
a fragmentation in the disintegrating process of the nucleolus, which has 
been so often described for other plants. Darling claims (loc. cit., p. 185) 
also that a spireme thread is well formed before synapsis, citing as evidence 
his Figs. 9, 10, and 11. In this respect I am unable to accept his inter- 
pretation, as I find prior to synapsis no indication of a spireme thread such 
as he figures. It is my conviction that Darling has in this instance mis- 
interpreted the sequence of steps in the process, an error which is so preva- 
lent in cytological literature dealing with plants. His Figs. 10 and 11 
are certainly post-synaptic stages if, as he claims, his Figs. 13, 14, and 15 
are post-synaptic. I do not consider the nuclear structure of Figs. 4 and 5 
as spiremes, but a network with meshes of varying sizes. The structure 
shown in Fig. 5 now passes directly into synapsis (Figs. 6 and 7). From 
Fig. 6 it is seen that the nuclear network tends to accumulate towards one 
side of the nucleus, and this accumulation may or may not include within 
itself the nucleolus. In the gradual contraction of the nuclear network the 
chromatin granules are brought closer together, some of the smaller ones 
doubtless collecting into larger ones. Likewise, some of the delicate linin 
threads of the meshes will be united and others severed. The synaptic 
contraction is the initiation of the spireme, and as the spireme is seen to be 
present as soon as any indication of a loosening up of the densely contracted 
mass is evident, it is difficult to understand how a spireme could be formed 
from a network in any other manner. The most that can be said is that, 
as the net contracts into the synaptic mass, there is a tendency to form 
a spireme. This tendency is more pronounced in some nuclei than in 
others, I find no support for the doctrine of Lawson (Tl) that synapsis 
is brought about merely by an enlargement of the cavity of the nucleus. 
There is no doubt whatever that we have to do with a real contraction 01- 
balling up of the nuclear network. 
Figs. 7 and 8 represent the earliest stages of complete synapsis. The 
granules are densely massed, yet it can be seen that there are distinct 
granules. In Fig. 10 the contracted mass appears to be made up of larger 
and coarser lumps. Although this cell is larger than Fig. 8 and the cyto- 
plasm gives evidence of rounding off, yet it is not possible to say that 
Fig. 10 is a later stage than Fig. 8, for the pollen mother-cells differ con- 
siderably in size, and there is considerable variation in the time of the 
rounding off of the cells. There is a possibility that fixation may be less 
perfect in cases like Fig. 10, as there may be different degrees of poor or 
faulty fixation. In Fig. 9 we have a stage in synapsis that is a little more 
advanced than that of Figs. 7 and 8. One large and one small nucleolus lie 
near the contracted mass, in which it may be clearly seen that a chromatin 
thread or spireme is in process of formation. At the stage of Fig. 9 the cell 
usually shows signs of rounding off at the corners preparatory to separation 
from the primary cell-wall of the mother cell (Fig. 11). In this, as in many 
