Sperm-Cells in Asclepias Cornuti ,. Decaisne. 129 
The Archesporium. 
Sections through young buds about 3 mm. in diameter 
showed the five young anthers around the central axis of 
the flower, each having two well-defined oval areas containing 
a varying number of large, long cells, arranged radially, and 
having comparatively large nuclei (PL VII, Fig. 1). These 
areas occupy the position of the pollen-masses in older buds, 
and so, evidently, locate the locules. 
Much younger buds were then sectioned until a stage was 
reached where there was no marked indication of differentia- 
tion of cells in the anther. Such a stage is shown in Fig. 2, 
where cell-division is taking place in various directions 
throughout the tissue. Soon, however, these divisions cease, 
and a row of sub-epidermal cells in each end of the anther on 
the proximal side appear larger and richer in protoplasmic 
content. They are usually straight, but at a later age some of 
them have a slightly sigmoid form. Division in these cells is 
always in periclinal planes, cutting off a sub-epidermal cell 
from an inner cell, which is later seen to give rise to the cells 
of the pollinium, and which will be referred to as the primary 
pollinium-cell (P"ig. 3). The division is shown complete in 
Fig. 4. This process varies from that described by Schacht 
(1853), who derived all the cells of a single pollinium from one 
primary mother-cell. 
The Tapetum. 
The sub-epidermal cells undergo many divisions in different 
planes, as shown in Fig. 5. Parallel with these changes the 
other tissue-cells immediately surrounding the primary 
pollinium-cells become altered, until finally a well-defined 
tapetal layer surrounds the primary pollinium-cells (Fig. 7). 
It is thus seen that in Asclepias the tapetum is a morpho- 
logical composite, as described by Coulter (1898) for Ranun- 
culus , by Caldwell (1899) for Lemna minor , and by Fulmer 
(1899) for Hemerocallis fulva. Frequently some of the 
primary pollinium-cells appear to disintegrate and function 
K 
