May, 1909.] Nuclear Divisions in Convallaria 505 



EXPLANATION OF PLATES XXIV AND XXY. 



All figures were made with the aid of a camera lucida. The 

 figures representing entire cells (excepting Fig. 20) were studied 

 with a B. & L. one-inch ocular and a 1-16 oil immersion objective; 

 Fig. 20, and all sub figures (excepting 20a) with a Zeiss No. 12 

 ocular and Leitz 2 m. obj.; Fig. 20a with the No. 12 ocular and 

 the 1-16 objective. 



Fig. 1. Microsporocyte with a very dense network of chromatin 

 matter; nucleolus visible, nuclear membrane distinct. 



Fig. 2. Microsporocyte with chromatin tibrils and definite granules. 



Fig. 3. Microsporocyte with thread contracting, the granules 

 spherical, linin definite, nucleolus deeply stained. 3a. A part of the thread. 



Fig. 4. More advanced stage; more granules noticeable. 



Fig. 5. Early synapsis, nucleus occupies most of the cell. 5a. 

 Granules are more oval. 



Fig. 6. Synapsis, thread free and continuous. 6a. Nticleolus shows 

 a clear area. 6b. Granules quite uniform in size, linin distinct. 



Fig. 7. Nucleus smaller, nucleolus pale and irregular, chromatin 

 matter contractinjj^ 7a. A part of the thread. 



Fig. 8. A later stage. 8a. The thread, some of the granules showing 

 a doubleness. 



Fig. 9. The contraction more advanced, the granules single, the 

 nucleus somewhat larger. The nucleolus very pale. 9a. A part of the 

 chromatin ribbon. 



Fig. 10. A microsporocyte with loops nearly developed. The 

 nucleolus apparently the center of activity. 10a. A separated, homo- 

 geneous band of chromatin matter. 



Fig. 11. The chromosomes nearly formed. 11a. Chromosomes 

 showing lobed ends and a differentiation down their median axes. 



Fig. 12. The sixteen chromosomes formed, micronucleoli in the 

 cytoplasm. 12a. Two chromosomes. 



Fig. 13. A sporocyte showing sixteen chromosomes. 



Fig. 14. Metaphase of first maturation division. 14a, 14b, chromo- 

 somes showing transverse divisions. 



Fig. 15. Late metaphase. 15a. Chromosomes showing transverse 

 divisions. 



Fig. 16. Telophase of heterotype division. 16a. Chromosomes 

 dividing. 



Fig. 17. Telophase of heterotype division, micronucleoli, wall, 

 plate, etc. 17a. A chromosome with lobed ends. 



Fig. 18. Late telophase, the resting chromosomes smaller than 

 in 17. 



Fig. 19. Metaphase of second division. Median split more notice- 

 able. 19a. Chromosomes dividing. 



Fig. 20. Metaphase of the homotype division, the mitoses simul- 

 taneous in the two daughter cells of the first division. 20a. Chromosomes. 



Fig. 21. Telophase of second division, chromosomes homogeneous, 

 no lobed ends. 21a. A chromosome. 



Fig. 22. A tetrad, the upper cell has not yet tmdergone a homo- 

 geneous division. 



Fig. 23. A spore-tetrad with common wall around the four cells. 



Fig. 24. An incipient pollen-grain. The dark body is the generative 

 nucleus. 



Fig. 25. Mature pollen-grain, generative cell with its clear cyto- 

 plasm at margin of the pollen-grain. 



Fig. 26. Telophase of a sporophyte division, showing long chromo- 

 somes, nucleoli scattered in the cytoplasm. 



7. 



