﻿348 BOTANICAL GAZETTE [may 



Wager (igoi): On the fertilization of Peronospora parasitica. Ann. Botany 



14: 263. 

 WISSELINGH (1900): Ueber Kerntheilung bei Spirogyra. Flora 87 : 355. 



EXPLANATION OF PLATES IX AND X. 



The material, fixed In weak chrom-acetic acid, was cut 'ii^ thick and 

 stained on the slide with safranin and gentian violet. All figures were 

 sketched with an Abb6 camera under the Zeiss apochromatic objective 2 mm. 

 or 1.5 mm. in combination with compensation oculars. The magnifica- 

 tion is as follows: Fig. i, 250 diameters; Figs. 2-5, 12, and 13, S^o 

 diameters; Figs. 6-9, 1,500 diameters; Figs. 10, 11, 14-29, 1,000 diameters; 

 Figs. 30-35, 667 diameters. 



PLATE IX. 



(Figs. 1-15 illustrate oogenesis.) 



Fig. I. End of hypha about to form an oogonium. 

 Fig. 2, Young oogonium, nuclei approaching spirem. 



Fig. 3. Central vacuole forming. 



Fig, 4. Central vacuole; nuclei in spirem. 



Fig. 5. More^advanced than Fig. 4; nuclei in mitosis. 



Fig. 6. Details of nucleus in spirem condition. 



Fig. 7. Metaphase of mitosis; spindle intranuclear; nucleolus outside of 

 spindle ; three chromosomes shown. 



Fig. 8. Mitosis just after the splitting of chromosomes at nuclear plate; 

 nucleolus outside the spindle. 



Fig. 9. Anaphase; two groups of chromosomes, four in each group, at 

 the poles. 



Fig. 10. Oogonium after mitosis with twice as many nuclei as previous 

 to that event. 



Fig. II, Oogonium older than in Fig. 10; nuclei degenerating. 



Fig, 12. Formation of ^^^ origins under low magnification (500 diame- 

 ters); coenocentrum in center of each ^^g origin. 



Fig. 13. Egg origins older than in Fig. 12 ; coenocentra with conspicuous 

 radiations. 



Fig. 14. Coenocentrum before Jthe differentiation of the egg origins; 

 radiations plain ; nucleus at one side of coenocentrum; other nuclei degene- 

 rating in the cytoplasm. 



Fig. 15. Similar to Fig. 14; two coenocentra; nucleus at the side of each; 

 many nuclei degenerating in the cytoplasm. 



PLATE X. 



(Figs. 16-29 illustrate oogenesis.) 

 Fig. 16. Egg origin just before rounding off to form ^^g\ conspicuous 

 coenocentrum with nucleus at the side. 



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