1899] DEVELOPMENT OF THE M1CROSPORANGIUM 333 
regularly three or four layers of cells differentiated entirely 
wound the sporogenous tissue. These stages were found in the 
autumn previous to the time of flowering, and all subsequent 
growth, both in the archesporium and in the wall, is due 
eitirely to the increase in diameter of the cells already formed. 
This was determined by an actual count of the cells in a great 
many cases, 
Inmost dicotyledonous anthers the archesporium becomes: 
distinct at a very early period. No such sharp demarcation 
exists, however, in the monocotyledons. In all of the cases 
‘tudied by the writer, and in those treated by Warming and 
Engler, the transition from the wall to the archesporium is so 
sradual, especially in the younger conditions, that only the most 
/ teotyled 
the 
r of 
‘ Ata slightly later period the fourth or innermost laye 
fea and 
ay . begins to enlarge. The cells grow considerably, 
\ in be mistaken for archesporial cells if it was not for 
: a. in the cytoplasm, This layer is the tapetum 
The |: : 
i history of the tapetal nucleus has been studied by 
