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1907] GATES—POLLEN DEVELOPMENT AND MUTATION gl 
and in which are embedded, especially near the margin, the “pro- 
chromosomes,” forming an incomplete circle around the periphery. 
The material in which are found the beginnings of this contraction, 
as well as its later stages, was fixed and stained in the same manner 
as the slightly earlier stages in which it does not occur. 
The transition from this stage to the regular spirem stages has not 
been followed. The pre-synaptic stages with a continuous spirem 
last for a comparatively long time, as shown by the frequency of 
their occurrence. The spirem is at first extremely delicate, very 
long and tangled (fig. rr). One large nucleolus is always seen at this 
time, but one or more smaller ones may also be present. In a later 
Stage the nucleolus is for a time closely appressed and somewhat 
flattened against the nuclear wall. Loops of the spirem extending 
to the wall frequently give a false appearance of doubling (fig. 14), 
but though a great many spirem stages have been studied, a double 
thread has never been observed. The small size of the nuclei, how- 
ever, and the delicacy of the spirem thread make it very difficult 
to determine this point. 
The spirem gradually contracts into a dense ball with a few 
loose threads projecting irregularly (fig. 12). In this closely con- 
tracted condition it may form a body about the size of the nucleolus, 
which can only be distinguished from the latter by its somewhat 
irregular outline (fig. 13). In the next stage observed the spirem is 
again loosely arranged in the nuclear cavity, but is greatly contracted 
in length and several times the thickness of the original spirem before 
the contraction stage. This is shortly before the spirem breaks up 
into chromosomes, and the thread is at this time about the same 
thickness ag the chromosomes in the later prophase. Throughout 
the earlier stages of the prophase the spirem thread is continuous, 
and, judging from its frequency, the duration of the long delicate 
spirem previous to the synapsis stage is considerably longer than 
that of the short thick spirem after synapsis and before it sce 
into chromosomes. In the latter stage, before segmentation into 
chromosomes, there is frequently found, besides the spirem, a ring- 
shaped body of chromatic material exactly like the spirem in thick- 
hess and staining power. This has evidently been cut off from the 
Spirem (figs. 17, 18, 19). Frequently there are two such rings. 
