the formation oi' cell-walls, and the tapetal colls 

 have tv^o or tliroe nuclei ^ach. (Tig. (3). The nuclei 

 of the pollen mother-cells increase in size both abso- 

 lutely, and as compared with the size of the mother- 

 cell. The nucleoli also increase notably, and the con- 

 tents of the cell become more larp;ely vacuolated (Fig. 

 7), The pollen mother-cells thicken their walls, and 

 soon float freely in the cavity of the anther. The 

 two tetrad divisions occur in very quick succession, 

 almost simultaneously (Fig.S), In this division the 

 nuclear processes do not show at all clearly, though 

 there is evidence of striae connecting the nuclei. The 

 v^alls of the separate pollen grains soon develop^, and 

 the grains are released by the using up of the mother- 

 cell walls. The mature grain was described by Von Mohl 

 in 1835 v/here he gives it a very short characteriza- 

 tion. It is shaped as an oblate spheroid, with three 

 meridional furi'ows (Pig. 9)between these furrows the 



