farr: cytokinesis of pollen-mother-cells 255 



servations, using as material the motlier-cells of Liliiim fixed in 

 Flemming's solutions and stained with the safranin, gentian-violet, 

 and orange G combination. It must be remembered that Stras- 

 burger's initial work was done on alcoholic material. Mottier 

 studied the process following the heterotypic nuclear division and 

 found that there is "eine auffallende Verdickung der Faden" in 

 the equatorial region. The mother-cell-wall is shown in his figures 

 to thicken meanwhile to about one twentieth of the diameter of 

 the cell. Strasburger (67g), from his study of Lilium and Alstroe- 

 meria, found that it is the fibers in the center of the spindle in 

 which the equatorial swellings first occur. The elements com- 

 posing the plate are pulled out and become extremely thin in the 

 middle; and as soon as they break a middle layer appears between 

 them. These equatorial swellings he had (67/) previously desig- 

 nated by the name, " Dermatosomen " ; but this term has not 

 been extensively used since then. Hof (30) in 1898 stated that 

 the cell-plate formation is accompanied by the shortening of the 

 fibers of the central spindle, but showed no drawings to support 

 this view. Wager (78) more recently has figured cell-plates in 

 the root-tips of Phaseolus. Davis (11) concluded that the fibers 

 involved in the formation of the cell-plates of the spore-mother- 

 cells of Anthoceros are not those of the central spindle which re- 

 mained from karyokinesis ; but that they are newly organized in 

 the cytoplasm after the disappearance of the latter. Mottier (446) 

 in 1900 modified his former opinion as to the origin of the cell-plate 

 in Lilium, and after a study oi Dictyota makes the following state- 

 ment: "That the cell-plate in the higher plants is formed by a lateral 

 union or fusion of the thickened connecting fibers may be seriously 

 questioned, for in some cases these fibers do not thicken very appre- 

 ciably in the equatorial region, nor do they lie sufficiently close to 

 one another to enable the slightly thickened middle parts to meet 

 and fuse . . . the conclusion seems justifiable, that the cell-plate is 

 formed by a homogeneous plasma which is conveyed to the cell- 

 plate region and deposited there by the connecting fibers." He 

 presents no new drawings of Lilium in support of this interpretation. 

 The most extensive and satisfactory study of cell-plate forma- 

 tion in the higher plants in recent years is that of Timberlake 

 (73) on the pollen-mother-cells of the larch and the root- tips of 

 the onion. The author found that the two types of cells are very 



