88 BOTANICAL GAZETTE [FEBRUARY 
guish between the cells of the middle layers and the tapetum by their 
appearance. 
This condition, where the tapetum breaks down early and the 
middle layer cells then grow in and fill up the loculus, is common 
and may occur in one loculus of an anther when the adjoining loculi 
show normal functioning tapetum. The ingrowth is frequently 
irregular, occurring more rapidly on one side of the cavity, thus causing 
the latter to lie excentrically in the anther lobe and to assume a narrow 
and flattened or irregular shape. This ingrowth of middle layer cells 
does not initiate the disintegration by pressure on the tapetal cells, or 
in any other way, for it only begins after the tapetum has more or less 
completely disappeared, which is long after the first appearance of 
degeneration in the tapetal cells. That the tapetal cells are necessary 
for the nourishment and growth of the pollen grains is shown by the 
entire absence of the latter in such cases long before the cavity is 
obliterated. 
Another and perhaps more common condition is for the tapetum 
to persist through the tettad divisions and until the persistent pollen 
grains attain a large size. The loculus meantime enlarges con- 
siderably by growth (jig. 7), and also by the flattening and breaking 
down of the middle layers, as would be expected in normal pollen 
_ development. The tapetal cells also generally become flattened at 
this time, and stretched out so as to line the larger cavity created 
partly by growth and partly by the degeneration of the middle layers. 
In such loculi pollen grains in various stages of development are fre- 
quently though not always found, although when present they almost 
invariably assume irregular and bizarre shapes, though they may con- 
tain nuclei which are normal in appearance. Rarely pollen grains 
may be seen which have the triangular disk-shaped appearance 
characteristic of the pollen in this genus; but such grains have never 
been observed to reach full size, although abnormally shaped grains 
may do so sometimes. 
It is evident that the break-down of the middle layers, as mentioned 
in the last paragraph, is due to pressure from the functioning tapetum, 
for the cells of the middle layer become flattened radially and lose 
their contents, while the tangential walls may persist for some time, 
forming irregular concentric rings of dark-staining substance. Later 
