Pollen Mother-cells of Li linm canadense . 199 
complete fusion of all the chromomeres of the thread until after the close 
of the synaptic period. Fig. 24, PI. VII, from a nucleus in the stage of the 
uniformly distributed spirem (shown in Fig. 23), shows such an apparently 
complete fusion. There now remains no evidence that the thread ever was 
anything other than a single structure, containing a single row of chromo- 
meres. In Fig. 24 there appears occasionally a small chromomere located 
near one edge of the thread, and it may be that these represent the occasional 
chromomeres of one fusing thread, already noted, which failed to find mates 
in the other thread. 
The chromomeres are imbedded in the linin, and seem to project from 
it slightly at the edges of the thread. To the projecting points a fine, short 
linin fibre can sometimes be seen to be attached. These fine fibres are not 
often easily distinguishable in iron-haematoxylin preparations, but in those 
stained with the triple stain (Figs. 19-21), they are more plainly visible. 
In the cells represented in Figs. 19-21, the internal structure of the thread 
is not apparent, but there appear on the surface of the thread two rows of 
external swellings or granules, usually quite small, but occasionally (as in 
Fig. 19) having a diameter equal to a third or even a half of that of the thread 
itself ; these swellings stain blue in preparations in which the thread, as 
a whole, is red, dark blue when the body of the thread is light blue or 
purple. The two rows lie on opposite sides of the thread, and for the most 
part are so arranged that each swelling in one row is opposite one in the 
other row. In preparations which show the internal differentiation of the 
thread into linin and chromatin, the position of these pairs of external 
swellings, where they can be made out, corresponds with that of the 
chromomeres. The swellings, therefore, are the projecting points of 
the chromomeres. These projections are not always differentially stained, 
even with the triple stain, and then do not show except as they give to the 
thread an irregular outline; but they are frequently very noticeable, 
especially on portions of the thread which lie comparatively free. From 
each one may be traced a very fine fibre extending out perpendicularly to 
the surface of the spirem thread, usually extremely short, but sometimes 
of considerable length. Where the attached fibres are of some length they 
may be seen, even in preparations in which the swellings are not differentially 
stained. I have not been able to distinguish these swellings nor the regular 
attachment of the fibres to the spirem before the fusion of the parallel 
threads ; but after the fusion they are of regular occurrence. 
Miss Sargant (’96, ’97) seems to have considered these external 
swellings to be the chromatin bodies themselves. She finds that at a very 
early stage the threads of the nuclear network contain a single row of dots ; 
this row becomes double during the transition to synapsis, as a result, she 
thinks, of a fission of each dot of the single row. The spirem is formed, 
therefore, with two rows of dots on opposite margins, which are separated 
