Sperm-Cells in Asclepias Cornuti , Decaisne. 137 
cell-plate curves back, the spindle-fibres spread out and 
radiate in all directions from the cell-plate. The ends of 
the fibres, except those attached to the nucleus, are free in 
the cytoplasm of the larger cell. These fibres shorten and 
finally disappear as the cell-wall develops, and the smaller 
cell is cut off quite completely from the larger one, though it 
does not become entirely free at first, as it is held by the wall 
of the pollinium-cell at the two points where this is joined by 
the newly formed wall (Fig. 31 a). Eventually this connexion 
disappears, and the smaller cell, surrounded by its own cell- 
wall, lies, as it were, in the little pocket of its sister-cell. The 
development of this cell-wall from the cell-plate seems to 
take place here much as described by Mottier 1 . By some 
unexplained process the smaller cell finally becomes com- 
pletely surrounded by the larger one. It seems as if the 
larger cell grew around the smaller one, the cell-walls of 
the former breaking down at the point where they come 
in contact, for later, the smaller cell lies more deeply within 
the larger cell, and is surrounded by a membrane distinct 
from itself. No conclusive evidence, however, was found in 
support of this theory. The membrane is shown around the 
spindle in Fig. 32. 
The nucleoli of both cells are relatively large and prominent 
objects, staining deeply with the gentian-violet (Fig. 31). No 
characteristic difference could be observed in the staining 
reaction of the two nuclei. 
The Origin of the Sperm-Cells. 
The nucleus of the smaller cell divides in the pollinium-cell 
and, so far as observed, this division is accomplished before 
the germination of the pollinium-cells,as described by Schaffner 
(1896) for Alisma Plantago , Wiegand (1899) for Potamogeton , 
Merrell (1900) for Silphium , and others. 
The nuclear spindle in this division is different from those 
observed in any of the other divisions. It is rather sharply 
1 Mottier (1897), p. 192 . 
