FARR: CYTOKINESIS OF POLLEN-MOTHER-CELLS 303 



cells were found which confirmed the figures of Strasburger with 

 respect to the row of granules in the equatorial plane ; but rarely, 

 if ever, were they as prominent as his drawings show them, and 

 they are arranged in chains and not in a plate. Furthermore, 

 other mother-cells were found which contained no such chain of 

 granules, or, if one was present, it lay in another part of the cell. 

 The hourglass-like figures which appear in Primula were also 

 noted in Tropaeolum. No evidence of a true cell-plate was found. 



There is in these pollen-mother-cells no indication of a centrif- 

 ugally formed continuous cell-plate such as is so conspicuous in 

 the pollen-mother-cells of the lily and the larch and in vegeta- 

 tive cells of the higher plants. The central spindle is poorly 

 developed and there is no shortening of its fibers. But the fact 

 that we have here, as in cell-plate formation, the close association 

 of the fibers with the formation of the plasma membrane, points 

 to the importance of the study of these structures in their relation 

 to the phenomena of cell-division. 



Further studies are contemplated, involving a wide range of 

 species and extending to the nuclear phenomena incident to 

 quadripartition. 



IX. Discussion 



The existence of a form of division by furrowing in certain cells 

 of the higher plants suggests the possibility of ultimately harmon- 

 izing the usual division by cell-plates in these forms with the 

 division by so-called constriction in the higher animals. As 

 noted above, there are in the lower plants and animals also types 

 of cell-division more or less intermediate between these two 

 extremes; and it seems highly probable that the processes involved 

 in these essential phenomena of cellular reproduction are deter- 

 mined by the fundamental physico-chemical properties of the 

 complex colloidal protoplasmic mass. The fact that in many cases 

 of quadripartition, as described above, there is a gelatinization of 

 the cell-wall just prior to the division of the cell by furrows indi- 

 cates that the cell-wall may be an important factor in controlling 

 such form changes as occur in division by furrows. This only 

 emphasizes the contention that botanists have no right to con- 

 sider the protoplast alone as the cell. The growing and dividing 

 cell of the higher plants should be thought of as a unit comprised 

 both of protoplast and cell-wall. It is certainly a striking fact 



