Archegonium ; and on Spermatogenesis in Poly trichum. 119 
and prominence of the nucleolus-like body and in the extreme fineness of 
the nuclear reticulum, and in Polytrichum the presence of ‘suspending 
threads ’, a close agreement is found with the nucleus in the root-tip 
of Phased us. 
The Formation of the Chromosomes. 
On the approach of division the nucleolus loses its compact rounded 
appearance, and the threads connected with it become thicker and stain very 
deeply (Figs. 13 and 14). This appearance strongly suggests the direct 
transference of the chromatin of the nucleolus to the nuclear reticulum 
by way of the radiating threads. Finally the whole of the chromatin 
is passed to the reticulum, certain parts of which are consequently heavily 
loaded with this substance. Fig. 1 5 shows a surface view of the reticulum 
in this condition. Meanwhile the chromatin appears to have increased 
considerably in amount. In favourable cases, after the distribution of 
the chromatin to the reticulum, a feebly staining matrix is seen to remain 
in the centre of the nuclear cavity, and still connected with the peripheral 
network by radiating threads (Fig. 17). This remaining part of the 
nucleolus becomes lost to view when the spireme is established. 
The gradual advance of the chromatin from the nucleolus, along 
the radiating fibres to certain threads of the peripheral network, differs 
sharply from the simultaneous appearance of this substance in all those 
parts of the thread system which form the chromosomes, as described 
by Martins Mano ( 13 ) in Phaseolus and Solarium . Some agreement is 
found, however, in Poly trichum with Wager’s ( 19 ) account of the behaviour 
of the nucleolus in Phaseolus during the prophase, where this author saw 
appearances which led to the conclusion that a considerable amount of 
the substance of the nucleolus is transferred to the chromosomes. The 
remaining portion of the nucleolus in the same plant was observed to divide 
into two lumps which travel to the poles of the spindle and ultimately dis- 
appear. Martins Mano ( 13 ) states that these polar masses are expelled 
into the surrounding cytoplasm. In Polytrichum a definite extrusion of 
chromatin was seen to take place only during the last division of the 
spermatogenic cells and from the resultant spermatids. These extrusions 
will be dealt with later. 
Certain peripheral threads are now seen to be considerably thickened ; 
between these occur fine anastomosing connexions, and already an appear- 
ance of continuity in the stout thread system can be distinguished (Fig. 16). 
As this thread becomes transformed into a spireme, the connecting fibres 
break down, and the whole structure appears to contract towards the centre 
of the nuclear cavity (Figs. 4 and 5). Meanwhile the nuclear membrane 
has become very indistinct. A marked elongation of the nuclear region is 
observed at this stage, and the clear part external to the spireme is crossed 
