JTichols, A morphological study of Juniperus communis var. depressa. 239 



Figs. 40 — 44. Development of male gametophyte. 



Figs. 40 — 42. Early stages in growth of pollen tube. X 480. 



Fig. 43. Pollen tube at conclusion of first year's growth, sbowing winter 

 condition. X 480. 



Fig. 44. Pollen tube soon after renewal of activity the following spring. 

 X 480. 



Plate XI. 



Development of male gametophyte (cont.). 



Fig. 45. Spirem of division of generative cell. X 640. 



Fig. 46. Body nucleus (b), and stalk nuclous (s) immediately after their 

 formation. X 640. 



Fig. 47. Body and stalk nuclei have passed down the tube, meeting 

 tube nucleus (t) midway. X 640. 



Fig. 48. Lower end of pollen tube, showing body cell with stalk and 

 tube nuclei. X 640. 



Fig. 49. The same, one week later. X 640. 



Fig. 50. Body cell with stalk and tube nuclei during growth of pollen 

 tube toward archegonia. X 640. 



Fig. 51. Tip of pollen tube shortly after reaching archegonial Chamber. 

 Stalk and tube nuclei are indistinguishable from one another. X 480. 



Plate XII. 



Development of male cells. 



Fig. 52. Tip of pollen tube shortly after formation of male cells. X450. 



Fig. 53. The same just before fertilization. The male cells have become 

 spherical. X 450. 



Fig. 54. Abnormal case where four male cells have been formed by the 

 division of one body cell. X 600. 



Fig. 55. Division of body cell nucleus — early prophase. A more 

 or less continuous spirem is present and the chromatin granules are paired. 

 X 1200. 



Fig. 56. Prophase. Formation of chromosomes and development of 

 spindle fibers. Beconstructed from two adjoining sections. X 1200. 



Fig. 57. Metaphase. The chromosomes are becoming oriented at the 

 equatorial plane and have already split longitudinally. Beconstructed from two 

 adjoining sections. X 1200. 



Fig. 58. Late telophase. Nuclei of male cells have been organized and 

 a wall is being laid down between the two cells. X 1200. 



Plate XIII. 



Development of the megaspores from the megaspore mother cell and the first 

 nuclear division of the germinating embryo sac. 



Fig. 59. Longitudinal section through nucellus shortly before pollination, 

 showing archesporial region. X 460. 



Fig. 60. Megaspore mother cell in synapsis — nearly a year later than 

 the stage represented in fig. 59. X 800. 



