MEIOSIS 215 



portions of the thread in direct contact with the nucleolus display 

 heavy chromatin thickenings in contrast with the fine thread of 

 the more remote parts. This condition suggests a transference 

 of substance from the nucleolus and its utilisation in thread forma- 

 tion ; the near threads being much thickened by the extruded 

 material. The nuclear condition in Fig. 77, D, is not composed of 

 separate loops lying free from one another, but is the still con- 

 tinuous reticulum. This reticulate condition of the post-synizetic 

 thread has not been previously recorded in plant cytology. At a 

 slightly later stage in nuclear development the thread becomes 

 more evenly distributed throughout the nuclear cavity, and the 

 chromatin thickening is nearly uniform over the reticulum. 



The method of chromosome formation is not typical of either 

 para- or telo-synapsis. The first indication of chromosome forma- 

 tion is the appearance of small chromatic beads upon the reticu- 

 lum, while the thread between the aggregations is very delicate 

 and pale-staining. The chromatin aggregations are irregularly dis- 

 tributed upon the reticulum (Fig. 77, E), and show great variations 

 in size. It was found impossible to say definitely whether a single 

 aggregation represents a future bivalent or univalent chromo- 

 some. Chromosome formation takes place by the flowing together 

 of the chromatin on the post-synizetic reticulum. After a time 

 the threads joining these aggregations are absorbed and the bi- 

 valents become independent of one another. 



The method of chromosome formation eventually falls into line 

 with that typical of telosynapsis. The homologous chromosomes 

 of several pairs can be seen connected end-to-end — in some cases 

 from their free ends — and a severed strand projects, indicating 

 incomplete absorption of the reticulum on which they were formed. 



According to Gates and Latter, the chromatin aggregations 

 shown on the reticulum indicate that neither a para- or telo- 

 synaptic scheme of reduction is in force in these forms. In the 

 earlier stages there is no pronounced parallelism of the reticulum 

 to be observed, but in early diakinesis there is union of certain 

 homologous chromosomes in telosynaptic formation. Thus, 

 though a tendency to ultimate end-to-end union of homologues is 

 evident, the method of pairing on the reticulum may take an inter- 



