274 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



plate with the mother-wall somewhat thickened. Three years 

 later von Mohl (43c) published figures of spore formation in the 

 same plant which indicate a division by constriction sometimes 

 accompanied by a cell-plate and sometimes not. 



In 1854 Pringsheim (53) prompted by the work of von Mohl, 

 to whom he refers in his preface, presented a study of bipartition 

 and quadripartition in pollen-formation. On page 54 he describes 

 the thickening of the mother-cell-wall by regular layers as in 

 collenchyma formation. In Althaea there is a quadripartition, 

 either monoplanal or tetrahedral, which appears first as "Tren- 

 nungslinien." Division, he says, is, however, accomplished by 

 the ingrowth of the mother-wall, as in the Conferveae. In figure 4, 

 plate IV, there is represented a monoplanal square, with a ridge on 

 the inner surface of each of the four sides of the mother-wall, 

 and a square area in the center. He does not adequately describe 

 this central square. From the following study it will be seen 

 that it is not unlikely that the central square represents a mass of 

 mother-wall material which has followed the constriction furrows 

 toward the center of the tetranucleate cell. In 1865 Rosanoff (56) 

 published a couple of figures, 24 and 25, of Acacia paradoxa in 

 which are shown successive bipartition, the second division of 

 which is accomplished by constriction, and invagination of the 

 mother-wall at right angles to the first division and beginning 

 first along the periphery on the mother-wall and only after a time 

 becoming apparent on the division wall of the heterotypic mitosis. 

 The author does not discuss the process. 



Hofmeister (326) in 1867 included in his book on the "Pflanzen- 

 zelle" certain studies of pollen-formation which have not been 

 followed up by later investigators and seem to have been quite 

 forgotten in the recent tendency to ascribe all division of plant 

 cells to the activity of a cell-plate. However, in the light of the 

 following study and of much evidence which has up to the present 

 remained quite isolated, it seems just to attribute to Hofmeister 

 priority in grasping the real situation as to the pollen formation 

 of dicotyledons. Not only did Hofmeister study Althaea rosea, 

 which had received so much attention previously, but he also 

 worked on the Cucurbitaceae and the Passiflorcae, in addition to 

 certain monocotyledons and Anthoceros. In the dicotyledons he 

 reported a centripetal quadripartition and figured it in Passi- 



