Cardiff: Synapsis and reduction 281 



* 



Acer platanoides L. 



This plant presented especially good material for study. The 

 chromosomes are few and there is an exceedingly large amount of 

 sporogenous tissue in one small flower cluster. The form has the 

 disadvantage, however, of having exceedingly small sporogenous 

 cells, as will be noted from the drawings. Only microsporangia 

 were examined, though both micro- and megasporogenous tissue 

 were examined in a few cases in A. Pseudo-Platcuuts, which ap- 



parent!} 



platanoides 



The winter is passed with the sporogenous tissue in the early 

 mother-cell stage. In this stage (figure i)the cytoplasm is exceed- 

 ingly dense and granular with a very few small vacuoles, and it 

 takes stain strongly. There is as yet no rounding-ofif of the cell-wall 

 and no intercellular space in the sporangium. The cells are all 

 characterized by a relatively large nucleolus which appears to con- 

 tain small vacuoles (figure i). The chromatin is small in amount 

 and is collected in small granules at the periphery of the nucleus, 

 sometimes, apparently, even pressed against the nuclear mem- 

 brane. Owing to this position of the chromatin the number of 

 these granules could not be determined. Figure i shows* only a 

 sectional view of the nucleus. Connecting the chromatin granules 

 are exceedingly fine linin threads which will also occasionally be 

 found running across the nuclear cavity ; in the latter case they are 

 usually in contact with the nucleolus. Occasionally at the point 

 of contact of linin thread and nucleolus the latter will be found 

 bulged out forming a small papilla. It was impossible to deter- 

 mine definitely the significance of this, though it suggested at once 

 the formation of the true chromatin thread from the material of the 



* 



nucleolus. In some preparations this nucleolar papilla looked 

 much like one of the small vacuoles escaping. Later, however, 

 in examining the same phenomenon in Claytonia virginica there 

 seemed to be very strong evidence that there is a flowing of ma- 

 terial from the nucleolus to the linin-chromatin threads. At this 



me 



threads with reference to each other. 



As development continues, the threads leave the periphery and 

 traverse the nuclear cavity in all directions (figure 2). The chro- 

 matin constantly increases in bulk, chiefly, it appears, by an in- 



