276 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



spindle fibers at the equator, but the evidence that these form a 

 plate is by no means convincing. When it is remembered that 

 this material was fixed in alcohol, and that Strasburger repeatedly- 

 expressed his opinion that the pollen-mother-cells of dicotyledons 

 were very unfavorable material for study, there arises a grave 

 doubt as to whether we are justified in accepting these drawings 

 as final proof of the existence of true cell-plate formation in this 

 species. In his discussion he recognizes an "Einschniirung" of 

 the mother-cell, and a thickening of the wall at the equator in the 

 form of a ridge. 



On division in the pollen-formation of other dicotyledons, 

 Strasburger gives a few fragmentary remarks. He noted quadri- 

 partition in Cucumis, Delphinium, Aconitiim, Glaiicium, Althaea, 

 and Bryonia, but gives no figures or descriptions of the process. 

 In his paper on Asclepias (67 h) in 1901, Strasburger showed a 

 peculiar condition, where successive bipartitlon of the pollen- 

 mother-cells results in a row of four cells. The mother-wall is 

 not thickened, in fact it is scarcely discernible in the drawing. 

 His only descriptions of the division processes are that they are 

 by cell-plates. The following year he published (671) his Cerato- 

 phyllum paper, in which he includes no description of cell-division 

 but only one figure, number 46. The mother-cells appear to be 

 closely packed, and to have very thin walls. A partition appar- 

 ently results from the heterotypic mitosis. The second division 

 may be either monoplanal or tetrahedral. 



A few papers have given rather good evidence of the existence 

 of cell-plates in the mother-cells of dicotyledons. Ernst and 

 Schmidt (15) recently found successive bipartition by means of 

 cell-plates in Rafflesia. It is stated that the nuclei may be arranged 

 either monoplanally or tetrahedrally. Frye and Blodgett (21) 

 in 1905 also reported successive bipartition in the pollen-mother- 

 cells of Apocynum. They do not discuss the details of the process, 

 but show that it may result in the four spores being arranged 

 tetrahedrally or monoplanally in a square, rhomb, pyramid, or 

 row. In the drawing of the monoplanal square they suggest the 

 existence of a cell-plate, following the homoeotypic karyokinesis. 

 The mother- wall is not shown to be thickened. 



In 1907 Lubimenko and Maige (40) described a peculiar division 

 in Nymphaea in which a cell-plate is formed after the heterotypic 



