farr: cytokinesis of pollen-mother-cells 279 



fornia Academy of Sciences a figure, 24, of Cobaea which shows a 

 pollen-mother-cell after the homoeotypic karyokinesis with the four 

 nuclei tetrahedrally disposed and not appressed to the plasma 

 membrane, though cytoplasmic division has not yet occurred. 

 The spindles are inflated and the mother-wall is about one thirtieth 

 of the diameter of the cell. There is a concavity of the plasma 

 membrane on one side of the mother-cell, a convexity on another, 

 and the third side is flattened. " Cell-plates are now formed in the 

 usual way " (p. 1 78) . Two years later there ( 8) appeared in the same 

 journal a paper by Miss Byxbee on Lavatera. Her figure 24, also 

 of a mother-cell, has four nuclei arranged in a monoplanal rhomb also 

 with the suggestion of five spindles between them. The mother- 

 cell-wall is here about one twenty-second of the diameter of the 

 cell, and there is no indication of the division of the cytoplasm 

 either by cell-plates or by furrows. Here also the statement is 

 made that "cell-plates are formed later on" (p. 69). This is the 

 only reference to cytokinesis in the paper. It is evident that the 

 statements as to cell-plates in both Cobaea and Lavatera must be 

 regarded as quite unreliable. 



Tischler has reported a number of instances of quadripartition 

 in pollen-formation, but has never described the details of the 

 process. In 1906 in connection with his study of sterile Bryonia 

 hybrids (74a), he gives a figure, number 7, of a mother-cell in 

 which quadripartition would no doubt occur. But he does not 

 refer to it in the text, nor does the drawing show the mother-cell- 

 wall. In the same year in his study of Ribes hybrids (74^), he 

 presents two figures indicating quadripartition, one tetrahedral, 

 the other rhomboidal. In 1908 in further work along this line, 

 he gives a number of similar figures (74c). Number 14 shows 

 the mother- wall thickened to about one fourteenth of the diameter 

 of the cell in Mirabilis. Number 19 indicates that bipartition 

 has occurred after the heterotypic division, the mother- wall 

 being about one twentieth of the diameter of the cell. In figure 71 

 he shows a tetranucleate cell of Potentilla, with the mother-wall 

 thickened to one tenth the diameter of the cell. Figures 99 and 

 100 show a like condition in Syringa. Of Mirabilis he writes (p. 

 44), " In nicht wenigen Fallen gelingt aber die Ausbildung der Zell- 

 platte nicht mehr: wir erhalten vierkernige Zellen." This con- 

 stitutes the only evidence which he gives of having seen cell-plates 



