466 
F. L. PICKETT 
the sporogenous tissue regardless of the part of the anther wall in- 
cluded. The tapetal cells are clearly differentiated from those of the 
anther wall by their denser cytoplasm and larger nuclei. After the 
last vegetative division of the sporogenous cells, the tapetal cells 
may be distinguished, although less easily, from the pollen mother- 
cells by their more vacuolate cytoplasm and by peculiarities of nuclear 
structure. Nuclei of pollen mother-cells show the finely divided 
Fig. 6. A group of almost mature pollen spores, S, and tapetal nuclei, TN, 
the latter showing the chromatin masses characteristic of late stages. The smaller 
and more regular nuclei represent those with lessened activity. The nucleus at A 
suggests simple division. These nuclei are from different parts of one anther 
section; only enough portions of pollen spores are shown to indicate relative size 
and position. X 1400. 
chromatin and delicate Hnin network typical of such nuclei, while 
the tapetal nuclei show larger and more irregular masses of chromatin 
(text figure 7). With the appearance of the close synaptic ball in 
the nucleus of the pollen mother-cell, the typical resting nucleus 
serves to mark each tapetal cell even when such a cell is, as occasionally 
found, entirely surrounded by sporogenous cells (figure i^). 
When the tissues are first differentiated the tapetal cells are closely 
packed together and show distinct walls and well vacuolated cyto- 
plasm. As the sporangial cavity enlarges through the extension of 
