levine: somatic and reduction divisions in DROSERiV 137 



as they were in the early anaphase stages. Radiating fibers 

 extending in all directions appear about each of the four nuclei. 



Cell division. — It is well known now (Guignard, '15) that the divi- 

 sion of the pollen mother-cell both in monocotyledons and dicoty- 

 ledons may be either by successive division or bipartition or by sim- 

 ultaneous division or quadripartition. In Drosera rotundifolia, D. 

 filiformis, and D. intermedia, both types of division were observed 

 as intimated above. While it may be said that the predominant 

 method is by quadripartition (Figs. 36, 37), successive bipartition of 

 the pollen mother-cell also appears. Cell divisions may follow at 

 once in the heterotypic division. As mentioned above, the 

 central spindle apparently remains unchanged but a cell wall is 

 formed. The nuclei now divide again and this is followed by cell 

 division so that four serially arranged pollen cells are formed 

 (Fig. 38). For quadripartition no cell wall is formed after the 

 first nuclear division. The nuclei divide again and after recon- 

 struction in the presence of both central and radiating spindle 

 fibers cell walls are formed simultaneously, cutting the cytoplasm 

 into four approximately equal parts. 



While successive stages of development of the cell wall through 

 a cell plate have been observed in the somatic divisions as men- 

 tioned above, no indication is found of the presence of a cell plate 

 in the divisions of the pollen germ cells. Farr ('16) finds that in 

 Nicotiana and certain other dicotyledons quadripartition is the 

 rule and that it is accomplished by furrow rather than a cell plate. 

 The mother-cell wall in these cases is markedly thickened and 

 fills the constriction furrow during the division. I have seen these 

 preparations and the appearances are different from that in Drosera. 

 Cannon ('03) and Samuelsson ('14) hold that cell division of the 

 pollen mother-cell is brought about by the constriction of the 

 cytoplasm as in the division in animal cells. If furrows are 

 present in Drosera they must be extremely narrow like those 

 shown in the slime moulds by Harper ('00, '14), which proceed 

 from the periphery to the center of the cytoplasm (Figs. 36, 37, 39). 



As suggested above, certain pollen mother-cells disintegrate. 

 The process of disintegration is comparable to that described by 

 Tischler ('06) for Bryonia and Syringa hybrid pollen. After 

 completion of the homoeotypic division the reconstructed nuclei 

 lose their nuclear membranes and the nuclear content and cyto- 



