.254 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



kinesis of higher plants, the assumption has become general that 

 such a structure is uni\ersally present in angiosperms, gymno- 

 sperms, ferns, and bryophytcs. Strasburger already in 1875 dis- 

 cussed the formation of the plate by fusion of thickenings on the 

 central spindle-fibers, its splitting to form the boundaries of the 

 daughter-cells, and the secretion of the cellulose wall or walls 

 between the new daughter-cell boundaries. Strasburger's views 

 have been critically confirmed and enlarged by Treub for the 

 orchids, ]\Iottier for the mother-cells of the lily, Hof for the root- 

 tips of Ephedra, Pteris, and Vicia, Nemec for Allium, and Timber- 

 lake for the root-tips of Allium and for the pollen mother-cells of 

 the larch. In addition to this critical work there has appeared 

 in the literature a vast numl)cr of more or less casual statements 

 corroborating this interpretation with regard to the cells of 

 various representatives of nearly all groups of the higher plants. 

 Apparently in only one instance has a serious attempt been made 

 to question the universal occurrence of cell-plate formation in 

 the cytokinesis of higher plants, namely, the work of Baranetsky 

 (4) in 1880 which has not been recognized as presenting such an 

 exception to this rule, doubtless chiefly because it does not 

 furnish the positive proof of how division may be accomplished 

 without a cell-plate. 



On the other hand, it has been just as carefully established that 

 the animal cell divides without the formation of a cell-plate in the 

 equator of the central spindle. Flemming's attempt to homologize 

 the "zwischenkorper" of certain animal cells with the cell-plate 

 of plants has not been generally accepted. The "zwischenkorper" 

 has not been shown to play any part in the formation of the new 

 plasma membranes, whereas this is recognized as a large part of 

 the function and acti\'ity of the cell-plate. 



Treub (75(/) in 187S presented the first careful observations of 

 cell-division in li\ing material. His findings, in general, agree 

 with those of Strasl)urger; but in Epipactis, he reports, the daugh- 

 ter nuclei tra\(l from one side of the eel to the other, while the 

 •cell-plate is being laid down progressively between them. lie 

 believed, however, that the cell-plate was of cytoplasmic origin. 



In 1887 Went (79) for the first time presented the idea that the 

 fibers in the center of the spindle disappear during the growth of 

 the cell-plate. Motlier (44a) in 1897 confirmed Strasburger's ob- 



