70 * BOTANICAL GAZETTE [January 



PLATE VII 



Figs. 18-25 magnified 700 diameters; fig. 26 magnified 800 diameters; 

 figs. 22 and 25 are V. hastata; all the others V. angustifolia. 



Fig. 18.— Details of ovule outlined in fig. 15, showing megaspore mother 



cell. 



Fig. 19. — Nucellus of older ovule. 



Figs. 20, 21. — Megaspore mother cell nucleus dividing into two (20), 



and four (21). . 



Fig. 22. — -Growth of fertile megaspore and its encroachment on sterile 



cells; nucellus cells somewhat stretched. 



Fig. 23. — Embryo sac with 2 nuclei. 



Fig. 24. — 'Embryo sac with 4 nuclei, reconstructed from 4 sections. 



Fig. 25.— Embryo sac with polar nuclei in contact. 



Fig. 26. — Details of a part of ovary outlined in text fig. 27, showing 

 mature embryo sac invested by jacket; proteid-like substance in space between 

 ovule and carpel. 



PLATE VIII 



Figs. 28-41 magnified 700 diameters; figs. 42-45 magnified 800 diameters; 

 figs. 42, 45 are V. stricta; all the others V. angustifolia. 



Fig. 28. — -Longitudinal section of young anther showing sporogenous cell 

 row and surrounding layers. 



Figs. 29, 30. — Transverse and longitudinal sections through an older 

 anther, showing granular and mostly binucleate tapetal cells: fig. 29, cells of 

 middle layer, also granular; fig. 30, some rows of pollen mother cells, with 

 nuclei in synapsis. 



Fig. 31. — -Three pollen mother cells in first division; tapetal cells with 

 2 nuclei. 



Fig. 32. — -Two pollen mother cells in anaphase of first division. 



Fig. 33. — Early telophase of second division in pollen mother cell. 



Figs. 34, 35. — -Tetrad formation; some cytoplasm of mother cell concerned 

 in wall formation. 



Fig. 36. — -Tetrad formation; cytoplasm of mother cell not concerned in 

 wall formation. 



Figs. 37-41.— Successive stages of development of pollen grain: fig. 39> 

 pollen with starch grains; fig. 40, pollen with large vacuole; fig. 41 > pollen 

 with vegetative and generative nuclei. 



Fig. 42.— Pollen tube just thrusting itself through nucellar cap. 



Figs. 43, 44. — Fertilization: fig. 43, male nuclei fusing with egg and endo- 

 sperm nucleus; pollen tube and starch grains shown. 



Fig. 45. — First division of primary endosperm nucleus followed by wall 

 formation. 



