THE WANDERING TAPETAL NUCLEI OF ARISAEMA 467 
its wall cells the tapetal cells show a tendency to pull apart and round 
up (text figures i and 2). This separation seems to indicate that 
normal extension of these cells has ceased and the continued enlarge- 
ment of the cavity has left them without external pressure, for measure- 
ments of the cells at this time compared with similar measurements 
made before their separation shows no appreciable shrinkage. At this 
time the middle lamella has entirely disappeared and in a short time 
the cells, rounded up and floating in the cell sap of the sporangial 
Fig. 7. Fig. 8. 
Fig. 7. A normal tapetal cell before the disappearance of the wall, showing 
the highly vacuolate cytoplasm, and characteristic nuclear structure. X 1400. 
Fig. 8, Almost mature pollen grains and a few persistent tapetal nuclei. 
X 1000. 
cavity, lose through hydrolization and solution all of their remaining 
cell walls. When the heterotypic division is completed the mass of 
pollen mother-cells is completely surrounded by the tapetal proto- 
plasm and free floating nuclei (text figure 3) . This mass of protoplasm 
immediately streams in between the dividing cells, surrounding each 
one and filling the entire sporangial cavity (text figure 4; plate XX, 
figure i). From this time until the spores separate, the pollen mother- 
cells and the forming tetrads are within large, vacuole-like spaces in 
the tapetal protoplasm. The spreading of the protoplasm through 
the sporangial cavity is accompanied or immediately followed by a 
migration of the tapetal nuclei and their approximately equal distribu- 
tion throughout the cavity. All this time the tapetal protoplasm or 
the periplasm of Hannig (191 1) has shown a highly vacuolate structure. 
