258 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



there are enough libers to form a cell-plate completely across the 

 cell, successive division results; while if the cell-plate does not 

 reach across the cell it is absorbed into the rest of the protoplasm 

 and the final division takes place simultaneously after the second 

 nuclear division." As noted later, Juel (3 5a) and Tangl (70) 

 have found similar incipient cell-plates in the pollen mother-cells 

 of Hemerocallis. Though, in the latter, they may not extend 

 from one side of the mother-cell to the other, they seem to reach 

 a condition of maturity as far as they do develop, and remain 

 suspended in the cytoplasm, not being absorbed, as Timberlake 

 reports for the larch. 



b. Cytokinesis in the algae 



The algae display a considerable range of variation in their 

 method of cell-division. Strasburger was disposed to regard a 

 number of them as having cell-division by means of a cell-plate; 

 but the evidence, so far presented, is by no means conclusive that 

 the division is as it has been found in the higher plants. However, 

 McAllister (45) in his study of so simple a form as Tetraspora 

 found a great similarity to the typical seed-plant habit of division. 



The cytokinesis of Oedogonium has been much studied but 

 without clear results. Strasburger (67a) claims that after the 

 nucleus divides in the center of the cell, something like a cell- 

 plate, consisting among other things of a series of black dots is 

 formed. Tuttle (77) and Wisselingh (83) have since confirmed 

 Strasburger's observations as to the presence of an equatorial 

 differentiation between the daughter nuclei. In the cell-division 

 of Spirogyra there exists a somewhat greater departure from the 

 cell-plate type. Strasburger (67a) early described the centripetal 

 development of a cross- wall in the form of a girdle at the equator 

 of the cylindrical cell. The girdle grows by the deposition of 

 material on its inner edge where starch granules accumulate. The 

 existence of true central spindle fil)crs running between the two 

 daughter nuclei is still doubtful. In Cladophora we have an in- 

 stance of division of a multinucleate cell without even the sem- 

 blance of a cell-plate. This was first observed by von IMohl (43a) 

 in his famous pioneer work upon the origin of the cell. In 1854 

 Pringshelm (53) reported the finding of a thin division wall before 

 the centripetal ingrowth is completed; but alxnit twenty years 



