PLATE IV. 



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

 the future equatorial plate, and showing longitvidinal fission. Xi!400. 

 Pinus rtgida. 



39. Transverse segmentation is completed ; and the distinct chromosomes 

 have become apparent at the equatorial plate of the multipolar diarch 

 spindle. X 1,400. Ptnus Siyobtis. 



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

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



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

 plate. X 1,400. Pitius Strobus. 



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



43. Early telophase of the second division. X Ij400. 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 3'oung microspores are dis- 

 tinctly differentiated, each surrounded by its own wall. Xit40O. 

 Pitius rigida. May 10, 189S. 



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, 1S98. 



(162) 



