Chromosomes in Pollen Mother-cells . 
3 X 9 
is to be recognized with any certainty save in exceptional cases. The 
regularity of the hollow spirem is more pronounced in Podophyllum than 
in many other plants observed by the writer, but the regularity is not so 
great as in those plants in which a diagrammatic arrangement of the 
thread into pole and anti-pole sides has been described. The stage of 
the regular, hollow spirem is followed by a tendency of portions of the 
chromatin thread to become arranged in long loops (Fig. 8) preparatory to 
passing into the second contraction, for a second so-called contraction is as 
certain in Podophyllum and in Lilium as there is a synapsis, although, 
as will be shown, this contraction is different in character and duration. 
The important thing to be borne in mind as regards Podophyllum is that, 
in the stage of the hollow spirem, we have a smooth and rather regularly 
arranged chromatin thread, in which all traces of a longitudinal split are 
obliterated save in exceptional cases, and consequently the sister halves of 
this thread do not diverge, as frequently happens in Lilium candidum . 
In Lilium . Turning now to Lilium Martagon and L. candidum , it 
will be observed that a similar sequence of events obtains here as in 
Podophyllum. Synapsis leaves the nuclear contents tightly massed or 
contracted into a ball, which, as a rule, lies close to the nuclear membrane 
at one side. In some instances the mass seemed to be more central in 
position. I was unable to determine any regularity in the location of the 
mass that might lead to the conclusion that the side against which it lay 
was determined by gravity. Very frequently, delicate colourless fibres or 
threads extend from the contracted mass to the nuclear membrane (Fig. 
24). Here also the loosening of the mass is first recognized by the 
extention of loops or turns of the spirem (Fig. 24). As in Podophyllum , the 
chromatin thread is seen to be double. This is especially apparent in 
cases where the halves of the spirem diverge for a short distance (Fig. 24, 
at the left). The loosening continues until the hollow spirem is reached 
(Figs. 25, 26). The turns of the spirem, though loosely arranged, are not 
disposed in any marked diagrammatic regularity. There are long and 
regular turns intermingled with short and abrupt curves and kinks. The 
spirem traverses the cavity of the nucleus as well as to follow its membrane. 
At this stage (Figs. 25, 26), usually one large nucleolus is present, but one, 
large and one or more smaller nucleoli may occur. In Lilium the chromatin 
spirem is very long and slender at the stage in question. In sections 
including an entire nucleus, it is not possible to follow the thread accurately 
throughout its entire course. Some parts will always be concealed by 
others, and for that reason I have made no attempt to represent the im- 
possible in a camera lucida drawing. Fig. 26 represents the larger part, 
but not the whole nucleus. It cannot be stated, therefore, whether free 
ends are present, but it is the opinion of the writer that the thread is 
endless, although this may be, and doubtless is, a matter of no importance. 
