Been — Studies in Spore Development. If. 709 
side of the nucleus. In the majority of cases there is now only a single 
large nucleolus, which sometimes lies pressed against the nuclear wall, but 
more often lies on the opposite side of the contracting reticulum. The most 
important alteration which can be seen to take place in the nuclear contents 
during the earlier stages of synapsis is the gradual transformation of the 
reticulum into a long, exceedingly delicate, and closely wound spireme 
(Figs. 5, 6, and 7). In no case have I found any indication of the occur- 
rence of chromatic bodies which could be interpreted as gamosomes or 
zygosomes. The nuclear cavity contains no other visible constituent 
besides the nucleolus and the system of delicate, closely coiled threads. 
The threadwork is so closely wound together that it is quite impossible 
for any one to find in it the slightest evidence in support of the occurrence 
of two systems of threads lying parallel with one another. It would be just 
as reasonable to claim that a dozen threads could be counted lying parallel 
with one another in this coil as to assert that two such can be seen thus 
arranged. Moreover, the few loops which, in some cases, stretch from the 
margin of the coil into the nuclear cavity, are most certainly single structures. 
It is only necessary to glance at Fig. 6, which gives a true representation of 
a nucleus of Doronicum at this stage, to fully realize that there is neither 
any evidence for the existence of two parallel spiremes nor for that of paired 
gamosomes within the synaptic coil. 
During synapsis the spireme becomes gradually thicker and at the same 
time shorter (compare Fig. 5 with Fig. 8, both of Calendula). In many 
cases this thicker thread appears quite uniform in structure, but where the 
differentiation of the stain has been carefully carried out, it can be seen that 
as the synaptic coil loosens and begins to open out, the filament exhibits an 
alternation of darker coloured areas (chromomeres) with lighter ones. The 
synaptic knot continues to unfold and passes into the stage of the hollow 
spireme (Fig. 11). 
Hollow Spireme. 
As in the later stages of synapsis, so here also the thread often appears 
homogeneous, but in both cases, when the differentiation of the stain has 
been properly regulated, the filament can be seen to have a definite structure. 
In these cases there is an alternation of darker and lighter areas which no 
doubt signifies that, as is the case with many other plants which have been 
studied by cytologists, the spireme of the Compositae also consists of a linin 
thread in which chromatic bodies (chromomeres) are embedded. I have 
observed this structure of the spireme in all the species of Compositae which 
I have closely examined. Fig. 9 shows a portion of the spireme of Calendida 
which exhibits this structure very clearly. 
The coils of the hollow spireme extend over the entire nuclear space 
as a series of broad, open loops. 
