18 Mitosis in Pellia 



38, Van Hook, J. M " Notes on the Division of the Cell and Nucleus in Liverworts." Bot. 



Gazette, Vol. XXX (1900), pp. 394-99, Plate 23. 



39. Webber, H. J. '* Peculiar Structures Occurring in the Pollen Tube of Zamia." Ibid., Vol. 



XXIII (1897), pp. 453-59, Plate 40. 



EXPLANATION OF PLATES 



All figures were made with a Bausch and Lomb camera lucida, Zeiss apochromatic 

 immersion objective 2 mm. 1.30 N. A., and Zeiss compensating ocular 12 ; magnification, about 

 1,500 diameters. All figures are from Pellia epiphylla, Raddi, except Figs. 1, 2, 11, and 12, 

 which are from Pellia calycina, Nees. 



PLATE XXV 



(Figs. 1-8, mitoses in germinating spore; 1-6, first mitosis, 7 and 8 third mitosis; Figs. 8 and 10, mitosis 



in apical region of thallus.) 



Fig. 1.— Area about the elongating nucleus has become rather free from starch grains and 

 larger granules. Asters and caps are present. 



Fig. 2. — Peculiar aster at upper pole; the papilla indicates that it is pulling upon the 

 nuclear membrane. 



Fig. 3. — The cap is very conspicuous and the nuclear membrane is still intact. 



Fig. 4. — A cap just beginning to break up into fibers. A transverse section at this stage 

 shows a ring. 



Fig. 5. — Transverse section of fully formed spindle. 



Fig. 6. — Mitosis in late prophase; the spindle is evidently made up of two half -spindles, 

 radiations conspicuous; definitely formed centrospheres are lacking. 



Fig. 7. — Metaphase of third mitosis; no radiations or centrospheres are present. Figures 

 of first mitosis are the same at this stage. 



Fig. 8. — Irregular mitosis (third mitosis) in an unusually large spore, suggesting how 

 nuclei with an irregular number of chromosomes might be formed. 



Fig. 9. — Mitosis near apical cell; caps prominent and radiations reaching to the Haut- 

 schicht ; at the upper pole is a granule resembling a centrosome. 



Fig. 10. — Anaphase in mitosis near the apical cell; no asters or centrospheres are present. 



PLATE XXYI 

 (Figs. 11-17, second mitosis; 18-20, third mitosis, in germinating spore.) 



Fig. 11. — Very early prophase. 



Fig. 12. — Centrosphere and radiations. 



Fig. 13. — Very prominent centrosphere and radiations. The centripetal ends of the radia- 

 tions have a pseudopodium-like aspect and suggest that the radiations are lines of streaming 

 material. 



Fig. 14. — Centrosphere in which the cut end of a fiber resembles a centrosome. There is 

 no centrosphere or aster at the other pole. 



Fig. 15. — Irregular, elongated centrosphere with prominent aster; no centrosphere or aster 

 at the other pole. 



Fig. 16. — Tripolar spindle, the third pole not shown. The cut end of a fiber resembles a 

 centrosome. The pull upon the nucleus is evident; upper aster at some distance from the 

 nucleus. 



344 



