1918] OTTLEY—IMPATIENS 301 
sporangia. Fig. 20 shows a cross-section of one-quarter of an 
anther when the nuclei of the microspore mother cells are in the 
synaptic state. The walls of the cells of the epidermis are cutinized 
and thicker than those of the other cells. The wall of the micro- 
sporangium consists of two distinct regions, the outer irregular 
portion made up of 1-5 layers of nearly isodiametric cells, and an 
inner region about 2 cells thick, the cells of which are flattened 
tangentially. This flattening, doubtless, results from the pressure 
caused by the growth of the archesporial and tapetal cells. 
The microspore mother cells are separated from this inner 
wall by the tapetal cells. The latter, however, are not limited 
to the peripheral region, but extend into the mass of sporogenous 
cells and in some cases ramify entirely through the loculus, occupy- 
. Ing more than one-half of the sporangial cavity. The origin of 
the tapetum was not definitely determined, but it seems highly 
probable that it arises from the sterilization of sporogenous tissue 
rather than from the inner cells of the wall, and that all of the 
sterile cells within the sporangium are of the same ancestry. The 
tapetal cells vary in size, many of them being as large as the micro- 
spore mother cells. They are binucleate and are more vacuolate 
than are the functional spore mother cells. The two nuclei.of a 
single cell are usually side by side either at the center of the cell 
or atoneend. Each nucleus contains one nucleolus or occasionally 
more. 
CALDWELL (11) describes a condition for Lemna minor in some 
respects similar to that just outlined. He finds that during the 
early stages of the heterotypic division the cells of the tapetum 
sometimes divide and form groups of cells which project into the 
mother cell region; that the number of microspore mother cells 
is not reduced by the presence of the tapetal cells, although only a 
comparatively few developed spores, the others disorganizing and 
aiding the tapetum in nourishing the functional mother cells. In 
I. Sultani only about half the number of microspore mother cells 
arise that one would expect from the size of the sporangium. As 
indicated, not all of the tapetal cells arise at the periphery of the 
sporogenous mass, but many of them originate side by side with 
the microspore mother cells. The small number of microspore 
