Cardiff : Synapsis and reduction 293 



other forms studied, though this may be due simply to the general 

 slow development in Botrychium. Differing from the other forms 

 described, the nucleus of Botrychium continues to increase in size 

 for some time after synapsis. 



As the threads come out of the contracted condition in synapsis 

 they are short and thick and show a bivalent character (figure 69). 

 They disentangle until they are uniformly distributed throughout 

 the nucleus (figure 70), meanwhile continuing to shorten and 

 thicken. Later they can be seen dividing transversely to form 

 the chromosomes (figure 71). These contract until in the later 

 prophase they are almost isodiametric (figures 72 and 7^), yet 

 practically all show a bivalent character. In fact, from synapsis 

 to metaphase of the first division, the bivalent character of the 

 threads and chromosomes is always evident. That the univalent 

 parts of these bivalents represent the threads which conjugated in 

 synapsis seems highly probable. 



Summary of results 



Synapsis is not an artifact, but a constant morphological char- 

 acter of the mother-cell. 



The synaptic knot is always around or in contact with the 



nucleolus. 



The unilateral position of the synaptic knot and nucleolus is 



probably due to gravity. 



There is a gradual increase in size of the nucleus up to the 



time of synapsis. 



There is an arrangement of chromatin into two or more threads 



previous to synapsis. 



The presynaptic threads arrange themselves in pairs, longi- 

 tudinally, and move together as synapsis is approached, finally 



fusing in synapsis. 



In the fusing of the threads the chromomeres generally fuse in 



pairs. 



Previous to synapsis the chromomeres are evident and 

 connected by a slender thread of linin. After synapsis the 

 thread is homogeneous throughout ; that is, there is a marked 

 difference in appearance of presynaptic and postsynaptic chro- 

 matin. 



