Figs. 43-48. (Original). Diagramatic outlines of embryo 

 sac and nuclear changes during fecundation modeled from 

 Guignard's descriptions. Fig. 43. Division of nuclei to form 

 the upper tetrad, showing asters eentrosomes, etc. Fig. 44. (a) 

 synergidse; (b) oosphere; (c) union of nuclei to form the 

 nucleus of the embryo sae. Fig. 45. (a) nuclei of the syner- 

 gidaj; (6) nucleus of the oosphere; (d) male pronucleus pre- 

 ceded by its directive spheres; (e) pollen tube. Fig 46. 

 Union of the male and female directive spheres. Fig. 47. 

 Separation of the directive spheres and union of nuclei. Fig. 

 48. Fecundated nucleus ready for the first segmentation, the 

 male portion is still distinguishable (the male nucleus in 

 the last three colored dark). 



Figs. 49-5G. (Redrawn from Guignard, Annal. des Sci. Nat, 

 Bot. Se. 7, T. xiv, PI. 10). Formation of the pollen grains in 

 a pollen mother cell of Lilium martagon. Fig. 49. Mother 

 cell in resting stage showing chromatin band, nucleolus (para- 

 nucleolus) and two directive spheres. Fig. 50. Rupture of 

 chromatin filament into 12 segments. Fig. 51. Division 

 (longitudinal) of these segments. Fig. 52. The nuclear 

 spindle in profile. Fig. 53. Separation of the daughter seg- 

 ments and division of the directive sphere. Fig. 54. Two 

 cells in the resting stage, completion of the first division. Fig. 

 55. Division of these two cells to form the four pollen grains. 

 Fig. 56. One of the young pollen grains of the last division 

 in a resting stage before the division which gives rise to the 

 vegetative and generative nuclei. (See Fig. 39.) 



Figs. 57-59. (Redrawn from Wagner, Ann. of Bot. vol. iv, 

 PI. vi.) Fecundation of Peronospora parasitica. Fig. 57. 

 Oogonium with antheridium at one side. Fig. 58. Formation 

 of oosphere, two nuclei approaching the centre to unite. Fig- 

 59. Mature oosphere in process of fecundation, showing the 

 antheridial tube grown through the oogonium to the oosphere. 



Fig. 00. (Adapted from Geddes and Thomson, 1. c.) Dia- 

 gram illustrating effect of environment on an amoeboid cell. 

 On the left, when subjected to preponderating katabolism, 

 yielding antherozooid. On the right wlu-n subjected to prepond- 

 erating anabolism, yielding oosphere. Medium conditions -in- 

 dicated by the central line of amoeboid cells. 



