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AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
contents and large nuclei, occupying each of the four lobes of the anthers. 
Soon the archesporium becomes differentiated (text fig. 2) as a layer about 
two cells in thickness, which is formed parallel to the surface of the anther 
and is covered by the epidermis and by a variable number of layers of 
parietal cells. The parietal tissue and the archesporium are derived from 
the same primary tissue of the anther, the sporogenous cells being dis¬ 
tinguished by their denser and more deeply staining protoplasmic contents. 
The archesporium (PI. XXV, fig. 1, A) consists of a rather extensive 
tissue extending practically the whole length of the anther and appearing in 
the cross section as a horseshoe-shaped area very clearly marked off from 
the surrounding tissue. Since the anther does not split open at maturity 
but allows the pollen to escape by a terminal pore, the parietal cells show no 
modification of the walls to aid dehiscence. The tapetal cells (fig. 1, T) 
are rather large, active-appearing cells which, however, do not stain so 
deeply as the archesporial cells and which contain some vacuoles. The 
adjacent parietal cells gradually become flattened, and after the organiza¬ 
tion of the pollen grains the entire tapetum and the inner parietal layers 
become disorganized. 
The nutritive cells on the inner side of the archesporial layer are very 
large and present the appearance of a glandular tissue (fig. 1, N). They 
constitute apparently the main source of supply of food material for the 
developing sporogenous tissue. The cell contents are less dense than those 
of the archesporium and contain large vacuoles distended with cell sap. 
Each cell at first contains a single nucleus, but by the time the pollen 
mother cells are developed most of the nuclei have divided, giving rise to 
large, binucleate cells. 
The archesporial cells divide several times and the daughter cells remain 
in rather close contact, thus forming somewhat indefinite groups of cells 
extending, as a rule, transversely across the anther locule (PI. XXV, fig. 2). 
The sporogenous cells finally increase considerably in size, lose their angular 
shape, and are then to be recognized as the microspore or pollen mother 
cells (PI. XXV, fig. 3, j). These give rise to the pollen grains by two 
divisions in rapid succession. Before the cells divide, however, the cell 
contents become somewhat shrunken away from the cell wall. The first 
division is the heterotypic division in which the chromosome number is 
reduced to one half that found in the vegetative cells. The second is the 
homoeotypic division and gives rise to the microspores which develop into 
the pollen grains. Owing to the small size of the cells, it was not possible 
to make out clearly all the stages of chromosome behavior in the nucleus in 
the prophase of the heterotypic division, but there is no evidence that the 
behavior differs from that described in other species. The formation of a 
spireme, the synapsis stage (PI. XXV, fig. 3, 2), the loss of the nuclear 
membrane (fig. 3, 3), and the separation of the chromatin material into 
chromosomes were observed, though the splitting of the spireme threads 
