Acer negundo , Z., and Staphylea trifolia , Z. 
131 
Publications referred to. 
As a discussion of the literature would greatly exceed the limits of this paper, only those 
contributions will be listed to which direct reference is made. 
Darling, Chester A. (’09) : Sex in Dioecious Plants. Bull. Torr. Bot. Club, vol. xxxvi, 1909 , 
PP- 1 7 7-99- 
Lawson, A. Anstruther (’ll) : The Phase of the Nucleus known as Synapsis. Trans. Roy. Soc . 
Edin., vol. xlvii, 1911, pp. 591-604. 
Mottier, D. M. (’97) : Beitrage zur Kenntniss der Kernteilung in den Pollenmutterzellen einiger 
Dikotylen und Monokotylen. Jahrb. f. wiss. Bot, vol. xxx, 1897, pp. 169-204. 
(’07) : The Development of the Heterotypic Chromosomes in Pollen Mother-cells. 
Ann. Bot., vol. xxi, 1907, pp. 309-47. 
(’69) : On the Prophases of the Heterotypic Mitosis in the Embryo-sac Mother- cell 
of Lilium . Ann. Bot., vol. xxiii, 1909, pp. 343-52. 
EXPLANATION OF PLATES IX AND X. 
Illustrating Professor Mottier’s paper on Mitosis in the Pollen Mother-cells of Acer negundo , L., 
and Staphylea trifolia , L. 
All figures were drawn from sections with the aid of the Abbe camera lucida with Zeiss 
apochromatic immersion 2 mm., apert. 1*40, and compensating ocular 12. Magnification about 
X 2,400. 
Acer negundo , L. 
Fig. 1. Tapetal cell during the early growth period of pollen mother-cells. 
Fig. 2. Tapetal cell at a later stage. The nucleus has divided. At the stages of Figs. 1 
and 2 the nuclei show a structure identical with that of the young pollen mother-cells. 
Figs. 3 and 4. Young pollen mother-cells, showing typical structure of nucleus and cytoplasm. 
Fig. 5. Slightly older than Figs. 3 and 4, showing nuclear structure just prior to synapsis. 
Fig. 6. The beginning of synapsis. 
Figs. 7 and 8. Complete synapsis. In both cases the nucleolus has not been included in the 
balled-up network. 
Fig. 9. The synaptic mass is beginning to loosen up, and a spireme is becoming visible. 
Fig. 10. A similar stage, in which the details are much less distinct. The synaptic mass is 
seen from the edge, or its more indefinite lumpy nature is partly due to the reagents. The cell has 
just begun to round off. 
Fig. 11. A later stage in the loosening up of the synaptic mass. The cell has rounded off, but 
the new cell-wall was not evident in this case. 
Fig. 12. Complete hollow spireme at the stage of its greatest regularity and uniformity. The 
cell is provided with its new thick and soft wall. No longitudinal split is to be observed in the 
spireme. 
Fig. 1 3. A step in what corresponds to the stage of the second contraction. 
Fig. 14. The spireme is partly segmented. 
Fig. 15. Segmentation just complete. 
Figs. 16, 17, and 18. Later stages. Fig. 16 represents a thick radial section, while Figs. 17 
and 18 are tangential. At this stage the bivalents seem to have attained their maximum size. 
K 2 
