442 ALpEN: LIFE HISTORY OF UVULARIA SESSILIFOLIA 
wall and primary sporogenous cell, FIG. 1, while the outer whorl 
of stamens has advanced to show several divisions of the primitive 
sporogenous cells as well as of the wall cells, F1G. 2. The general 
four-lobed appearance of the younger set is seen by reference to 
FIG. 3, and the comparative advance of the outer whorl noted in 
FIG. 4. (The crowding of the stamens is particularly noticeable 
at this time, which would account for the irregularity of outline 
in FIG. 4.) This earlier development of the outer set of stamens 
is noted in the history of the development until at the time of 
tetrad formation, the two are very nearly synchronous. The 
stages of the individual cells throughout any single anther are 
practically simultaneous. 
The differentiation of the hypodermal cell is the usual one, 
namely, the increased size and denser cytoplasm, FIG. 5. The 
number of primary archesporial cells may be from three to six, 
FIG. 1,2. In the young sporogenous cells the chromatic material 
is apparently very abundant, irregularly distributed in the fine 
linin mesh with prominent knots at the crossings. Two nucleoli 
are noted as of frequent occurrence, a condition that persists 
up to the mother cell stage, ric. 5. The tapetal cells were not 
differentiated at this stage. 
The primary wall cells divide to form five layers, the ues 
outermost making up the permanent wall of the sporangium, 
FIG. 6, the innermost functioning as tapetum, while the inter- 
vening one breaks down at the time of maturity of the microspore 
mother cells. The tapetal jacket cells round off with the spore 
genous mass, and at the time just preceding synapsis are usually 
elongated, the nuclei all in the end next the sporogenous USSiS 
FIG. 7. The nuclei of the tapetum are apparently at this ume 
about to disorganize, staining diffusely and appearing as oy 
masses. 
The mature spore mother cells, seen about th 
September, have so increased in size that the prominent 1¥ k 
is now the size of the original hypodermal cell. The linin netyyr 
of the nucleus is finer and the chromatin more evenly distributed, 
although still prominently knotted, than in the primitive sporo- 
genous cells. The nucleolus (frequently two appear) - sae? 
nent. By the latter part of September the spore mother cells 
the outer whorl of stamens show synapsis. 
e middle of 
cleus 
