PLATE IV. 



FIG. 38. Origin of the second spindle ; the chromatic band looped in region of 

 the future equatorial plate, and showing longitudinal fission. XM. 

 Pinus rigida. 



39. Transverse segmentation is completed ; and the distinct chromosomes 

 have become apparent at the equatorial plate of the multipolar diarch 

 spindle. X 1,400. Pinus Strobus. 



40. Separation of the daughter-chromosomes of each pair formed by the 

 transverse division shown in figure 39. X 1,400. Pinus Strobus. 



41. Daughter-chromosomes arranged in two parallel rows at the equatorial 

 plate. XMOO. Pinus Strobus. 



42. A late anaphase in the second division. X 1,400. Pinus Strobus. 



43. Early telophase of the second division. X 1,400. Pinus Strobus. 



44. Late telophase of the tetrad division ; the chromosomes of each nu- 

 cleus have fused to form a spireme, but the nuclear membrane is not 

 yet developed ; rather faint cytoplasmic threads connect the four nu- 

 clei ; the centripetal thickening of the mother-wall becomes more 

 apparent. X 1,400. Pinus rigida. 



45. The tetrad division is completed and the young microspores are dis- 

 tinctly differentiated, each surrounded by its own wall. X 1 ^ 00 - 

 Pinus rigida. May 10, 1898. 



46. The four microspores are separated by very prominent walls which 

 are continuous with the broad wall lining the original wall of the 

 microspore-mother-cell ; the outer, original spore-mother-wall is sepa- 

 rated at two points from the thick, more recently formed inner wall. 

 X 1,400. Pinus austriaca. May 9, 1898. 



47. Microspores still within the mother-wall and showing the beginnings 

 of the wings or air-sacs. X 1,400. Pinus Strobus. May 30, 1898. 



48. Rupture of the mother-wall and escape of the microspores. X Sio. 

 Pinus Strobus. May 30, 1898. 



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