290 Cardiff : Synapsis and reduction 



culty, it did not prove as profitable a form for study as some of 

 the others which were used. 



The nuclei contain a great abundance of chromatin which in 

 the very early mother-cell is in a coarsely reticulate condition. In 

 this stage, however, can be seen evidence of both chromomeres 

 and linin, often in a thread-like arrangement (figure 52). No 

 regularity in the arrangement of these thread-like masses of chro- 

 matin can be discerned except that they appear more abundant 

 near the periphery of the nucleus. There are present several 

 nucleoli which are generally surrounded by a clear area free from 

 chromatin. This condition I have found to obtain in the early 

 mother-cells of a number of other forms. There seems to be no 

 attraction or connection between chromatin and nucleolus as is 

 found so often in later stages. In fact this behavior of the chro- 

 matin toward the nucleolus and also the common arrangement of 

 chromatin at the periphery of the nucleolus indicates that, at this 

 stage, there may be a mutually repellant force existing between the 

 chromatin units, or perhaps groups of units. Nor is there anything 

 unreasonable in this idea, if, as is believed by many cytologists, 

 the maternal and paternal chromatin remain separate during the 

 presynaptic period of the first generation. 



The relative amount of cytoplasm in the microspore mother- 

 cells is exceedingly small as compared with any other form ex- 

 amined (figure 53). 



As the development proceeds the chromatin leaves the nuclear 

 wall and definite spireme threads are formed. Very shortly fol- 

 lowing this, the threads can be seen arranged in pairs (figure 53), 

 and show a differentiation into linin and chromatin. At this stage 

 the moieties are very seldom in contact. The threads do not 

 appear to be continuous in these early stages though they do 

 later. They change gradually from ragged, irregular, discontin- 

 uous threads to those of a more continuous, even outline and are 

 of a deeper staining capacity. In these threads the chromomeres 

 show quite clearly. Owing to the difficulty of showing all of the 

 chromatin of a nucleus at this stage only sections of nuclei are 

 figured (figures 53 and 54). In these later stages there is seldom 

 more than a single nucleolus, which is, however, always much 

 larger than any one of the nucleoli found in the earlier stages. 



