farr: cytokinesis of pollen-mother-cells 273 



wall in Hemerocallis, but the same year Strasburger (67c) pub- 

 lished the statement that the cell-wall is constructed after the 

 first division in this form. Juel (3 5a) in 1897 presented a long 

 paper in which he showed that the cell-plates after the heterotypic 

 karyokinesis in Hemerocallis are incompletely developed and 

 remain suspended in the cytoplasm. The same writer later (356) 

 reported^eph emeral c ell -plates in Carex af ter both the heterotypic 

 and homoeotypic karyokineses. _ In Zea Mays Kuwada (3 7) has 

 reported that after the heterotypic karyokinesis the mother-cell 

 occasionally constricts without the formation of a cell-plate 

 (text-fig. 2) ; this he associates with a subsequent amitosis and the 

 frequent abortion of the pollen. He found the peculiar constric- 

 tion in only two preparations. In Musa Tischler (74J) describes 

 (p. 637) the daughter cells after the heterotypic nuclear division as 

 "durch Plasmamembranen vonelnander abgegrenzt." The 

 daughter-cells re-divide several times in various planes, forming 

 either a row, a sphere, a square, a rhomb, etc. 



j. Pollen-formation in dicotyledons 



The evidence regarding the formation of cell-plates in the pollen- 

 mother-cells of dicotyledons is even more variable and fragmentary, 

 though the authors' statements are frequently very positive. 

 Naegeli (47) in 1842 was the first to publish on this point. For 

 Oenothera he shows a figure of tetrahedral quadripartition, in 

 which the mother-cell-wall Is thickened. He figures a similar 

 condition for Cucurbita Pepo and Bryonia, in the latter case 

 showing an evident constriction. He describes the process only 

 briefly, "auf der Innern Oberflache der Membran sechs vor- 

 springende Leisten ; dann plotzlich die Bildung von Scheidewanden, 

 die sich In Centrum beriihren." He believes, however, that the 

 dividing layers are of the nature of cell-plates and not ingrowths 

 of the cell-wall, as he attempted to show by plasmolysis. 



In 1850 Wimmel (82) confirmed the observation of Naegeli on 

 Oenothera and added studies on two or three other genera. In 

 Convolvulus he found that the division is accomplished by a fur- 

 rowing and shows a figure of the process. The mother-wall is 

 considerably thickened. In Momordica Elateriiim he found a 

 successive division, and figures the mother-wall here also as some- 

 what thickened. In Althaea rosea he figures a division by cell- 

 19 



