972 Davis.—A Comparison of the Reduction Divisions of 
Rosenberg, O. (’ 04 ): Ueber die Individualist der Chromosomen im Pflanzenreich. Flora, xciii, 
1904, p. 251. 
- ( 05 ): Zur Kenntnis der Reduktionsteilung in Pflanzen. Bot. Not., Part i, 1905, 
pp. 1-24. 
- (’09 a) : Znr Kenntnis von der Tetradenteilung der Compositen. Svensk Bot. 
Tidskrift, iii, 1909, p. 64. 
- (’09 £) : Uber den Ban des Ruhekerns. Svensk Bot. Tidskrift, iii, 1909, p. 163. 
Schouten, A. R. (’ 08 ) : Mutabiliteit en Variabiliteit. Groningen, 1908. Ref. Bot. Centbl., cviii, 
1908, p. 246. 
Stomps, T. J. (TO) : Kerndeeling en synapsis bij Spinacia oleracea , L. Amsterdam, 1910. 
EXPLANATION OF FIGURES IN PLATES LXXI-LXXIII. 
Illustrating Professor Davis’s paper on the Reduction Divisions of Oenothera Lamarckiana and 
Oenothera gigas. 
All figures were sketched with the aid of a camera lucida under the Zeiss apochromatic objective 
1.5 mm. (num. aper. 1*30) in combination with the compensating ocular No. 12, giving a magnifica¬ 
tion of 2,000 diameters. Sections cut 6 /a thick, and stained with iron-alum haematoxylin. 
PLATE LXXI. 
Figs. 1-31, Oenothera Lamarckiana. 
Fig. 1. Telophase following a mitosis in an archesporial cell, chromosomes still evident. 
Fig. 2. Resting nucleus in a pollen mother-cell showing large nucleolus, chromatic bodies, and 
delicate reticulum. 
Fig. 3. The chromatic bodies are no longer easily recognized in the denser reticulum. 
Fig. 4. Nucleus filled with a dense reticulum shortly before the advent of synapsis; chromatic 
bodies no longer distinguishable. 
Fig. 5. The beginning of the synaptic contraction, two nucleoli. 
Figs. 6 and 7. The synaptic contraction well underway, the threads and meshes of the reticulum 
becoming drawn into a close mass. 
Fig. 8. Two pollen mother-cells, their nuclei in mid-synapsis. 
Fig. 9. A closely contracted synaptic knot. 
Figs. 10 and 11. The thickened threads which emerge with the loosening of .the synaptic knot. 
Fig. 12. Further shortening and thickening of the threads to form the spireme. 
Figs. 13 and 14. Spireme with constrictions which show that the process of segmentation has begun. 
Figs. 15 and 16. Segmented spiremes, the chromosome segments for the most part clearly 
arranged end to end to form a chain. 
Fig. 17. A segmented spireme in a somewhat complicated looped arrangement. 
Fig. 18. Two chromosome segments in the form of a ring separated from the main group which 
is apparently in the stage of the ‘second contraction’. 
Figs. 19 and 20. These illustrate the stage of ‘second contraction’. The segments of the 
spireme are gathered in a close mass that bears a superficial resemblance to the synaptic knot. 
Fig. 21. Another form of the ‘ second contraction ’, the spireme segments more loosely associated. 
Fig. 22. Early prophase of the heterotypic mitosis. The nuclear membrane has disappeared 
and the nucleolus is no longer present; fourteen chromosomes could be counted, most of them still 
clearly arranged end to end. 
Figs. 23 and 24. Multipolar spindles; the chromosomes closely clustered as though still in the 
condition of the ‘ second contraction ’. 
Figs. 25 and 26. The spindles have become bipolar. Most of the chromosomes show the end- 
to-end arrangement; fourteen may be counted in Fig. 25. 
Fig. 27. Metaphase of the heterotypic mitosis. The chromosomes, now bent in the form of 
thickened V’s, show no close association in pairs. 
Fig. 28. Anaphase of the heterotypic mitosis. Seven chromosomes are present in each of the 
two sets which pass to the poles of the spindle. 
