farr: cytokinesis of pollen-mother-cells 275 



flora. In addition to observing the living material, means were 

 used for studying the wall and protoplast separately. He 

 dissolved the wall by means of sulphuric acid or copper-oxy- 

 ammonia, whereupon he could see the constriction furrows in the 

 plasma membrane independent of the cell-wall. On the other 

 hand he plasmolyzed the cell-content and in this way assured him- 

 self that the rjdges upon the inner surface of the cell-wall grow 

 centripetally to cut the protoplast into the daughter-cells. As 

 noted above, in Iris he induced division by causing the mother- 

 wall to swell in water, but he does not report the repetition of 

 this for any dicotyledons, though he did induce the cell-walls to 

 swell. On page 71 he states that the gelatinization of the cell- 

 wall permits the enlargement of the protoplast. If, however, the 

 inner layers only swell, the cell-content is compressed. In addi- 

 tion to quadripartition he also reports bipartition by cell-plate in 

 Passiflora. 



Seven years later Sachs (59) presented a whole series of figures 

 of quadripartition in the pollen-formation of Tropaeoliim minus. 

 These are evidently drawn from living material and show various 

 conditions of shrinkage and collapse of the protoplast, which, as 

 will be shown later, do occur in material crushed out under the 

 cover-glass. The drawings show very well the thickened wall, 

 and the centripetal formation of the cross-walls. In his discussion 

 Sachs does not agree exactly with the interpretation of Hofmeister 

 and conceives of quadripartition being brought about by absorp- 

 tion of the heterotypic cell-plate and the reconstruction of it in 

 addition to the formation of other cell-plates after the homoeotypic 

 karyokinesis. He says that quadripartition in Tropaeolum occurs 

 by the ingrowth of the mother-cell-wall at its junction with the 

 cell-plates. He, however, does not support this contention by 

 drawings. 



Strasburger followed the next year with his famous work on the 

 formation of cell-plates (67a -{- b) in a great many plants, in 

 w^hich he included drawings of what he interpreted as cell-plates 

 in the pollen-formation of Tropaeolum majus. This is the most 

 complete series of stages in division of the pollen-mother-cells of 

 any dicotyledon that Strasburger has ever published, his other 

 studies presenting merely single drawings. A careful survey of 

 these drawings of Tropaeolum reveal apparently swellings of the 



