194 Sargant . — Formation of the Sexual Nuclei 
drawn, it can be seen that the chromatic threads have grown 
in thickness. Sections from material fixed in Flemming’s 
solution show the structure of the thread in detail. It is 
irregularly thickened : here and there drops of nucleolar 
matter adhere to it (n, n, in Fig. 2 a). In the broader bits of 
thread from very clearly stained preparations, a double row 
of dots can sometimes be made out. 
The nucleus of the pollen-mother-cell has now entered on 
the period of contraction called synapsis, which precedes the 
formation of the spirem-thread. It is a condition which 
persists for several days, and the phenomena which distinguish 
it are familiar to all who have worked at the subject ; but it 
has been considered by most observers to be an artificial state 
produced by the action of reagents. This is not the place in 
which to enter into an account of the controversy which has 
arisen on various points connected with this subject. I shall 
simply describe my own observations on this period in the 
history of the pollen- mother-cell in the single case of Lilium 
Martagon. A fuller account of the evidence will be given 
than would be necessary if no controversy existed. 
The appearance of the nucleus in the contracted state 
depends very much upon the thickness of the section ex- 
amined. If it is thick enough to include the whole depth of 
most of the nuclei contained in it, the general appearance 
of each is that shown in Fig. 3, which is drawn from a hand- 
section of alcohol-material. All that is visible of each nucleus 
in such a section is a swollen nuclear cavity containing a ball 
of chromatic substance, which adheres to one side of it. The 
ball is clearly formed of close coils ; some of them can be 
distinguished from each other near the edge of the ball. No 
definite nuclear membrane can be made out ; but this is not 
conclusive in such a preparation, for its thickness necessarily 
renders details indistinct. 
Before proceeding to a description of thin serial sections, 
which give details of the nuclear structure in this stage with 
great precision, I will give a complete account of those 
observations on living material which have been mentioned 
