Sperm-Cells in Asclepias Cornuti, Decaisne . 14 1 
Summary. 
1. The individual cells of the pollinium of A. Cornuti are 
true pollen-grains which never become free. 
3. The divisions of the pollen-mother-cell are successive, 
and the spindles of the two divisions are oriented with their 
long axes radial and in the same line, so that each pollen- 
mother-cell gives rise to a row of four pollen-grains radially 
arranged. 
3. The outer membrane of each pollen-grain is composed 
of the wall of the mother-cell (which does not dissolve), plus 
the cross walls formed by the two divisions of the mother-cell. 
4. Each pollen-grain possesses an inner membrane which it 
develops about itself. 
5. The generative cell divides, before the formation of the 
pollen-tube, into two sperm-cells, each of which travels down 
the pollen-tube, passing the vegetative nucleus on the way. 
The above investigation was carried on in the Botanical 
Laboratory of Cornell University, and the writer wishes to 
express his best thanks and sincere appreciation to Professor 
G. F. Atkinson for exceptional opportunities offered by him, 
and for his constant encouragement and helpful suggestions. 
Ithaca, N. Y. 
Addendum : — Since the above paper was completed, Dr. 
Scott has called my attention to Corry’s work on Asclepias 
(1883, 1884) 1 . This writer agrees with Schacht in considering 
the archesporium as unicellular. From the archesporial cell 
are derived by successive divisions in different planes the 
pollen-mother-cells (‘ primitive mother-cells ’) . The pollinium 
is composed of the special mother-cells, which are formed by 
1 Corry, T. H., On the Mode of Development of the Pollinium in Asclepias 
Cornuti , Decaisne. Trans. Linn. Soc., London, 2nd Ser., Bot., vol. ii, p. 75, 1883. 
On the Structure and Development of the Gynostegium, and the Mode of 
Fertilization of Asclepias Cornuti , Decaisne ( A . syriaca , L.). Trans. Linn. Soc., 
London, 2nd Ser., Bot., vol. ii, p. 175, 1884. 
