1901] DEVELOPMENT OF THE POLLEN 331 
1 and 2, and Zeiss compensating 4, 8, 12, and 18. All drawings were 
sketched with a Bausch and Lomb camera lucida, 
Figs. 1-4. <Ascleptas Cornutt. 
Fig. 1. Cross section of young stamen showing archesporium just begin- 
ning the division into primary wall and primary sporogenous layers ; some- 
what diagrammatic. X 290. 
Fic. 2. Part of fig. 7, through archesporium. X 800. 
Fig. 3. Section across a stamen showing primary sporogenous cells 
grading into vegetative cells and division of primary wall layer into four 
layers ; partly diagrammatic. X 290. 
Fic. 4. Part of fg. 7, showing tapetal nature of cells surrounding the 
primary sporogenous cells. X 800. 
. Figs, 5-16. Asclepias tuberosa. 
Fic. 5. Longitudinal section through stamen showing location of spo- 
rangium and orientation of cells within; 4, hood; partly diagrammatic. X 22. 
Fic. 6, Longitudinal section of lower part of sporangium; two spore 
mother cele undergoing first division; one nucleus in aster stage, the other 
with chromosomes just split. x 800. 
1G. 7. Synapsis stage of nucleus in spore mother cell. X 800. 
Fig. 8. Aster stage in division of a vegetative cell. X 2150. 
FiG. 9. Axial view of plate of chromosomes in aster stage in vegetative 
cell. X 2150. 
Fic. 10, Longitudinal section of ee near its top showing second 
division of nucleus of spore mother cell. X 
Fic. 11. Section of young microspore ae thready protoplasm ; 
tapetal cells adjacent. x 800. 
IG. 12. Section of microspore containing masses of denser seen sie ; 
walls already thickened; tapetum adjacent. X 800. 
Fic. 13. Section of microspore; 4, deeply staining bodies; g, generative 
nucleus; /, tube nucleus. 
1G. 14. Section of microspore showing generative nucleus (g) flattened 
against the wall of the cell and just cut off. < 800. 
Fic. 15. Section of a generative cell cut off from the rest of the micro- 
Spore by a considerable wall. x goo 
Fig. 16. Section of microspore containing what may be a fragmented 
tube nucleus; x, side torn from pollinium wall. x 800. 
Q 
Fig.17. Ascleptas tncarnata, 
Fig. 17. Sketch of two pollinia germinating in a Io per cent. solution of 
cane sugar; partly diagrammatic. x 
