PLATE V. 



Fig. 49. Empty wall of the microspore-mother-cell showing the compartments 

 formerly occupied by the microspores. X Sio. Pinus Sirobus. 



50-54. Stages in the growth of the microspore ; the inner, partial wall 

 very apparent in the mature spore. Fig. 53 represents a section 

 through the middle of a young microspore in a plane perpendicular 

 to the wings. X Sio- Pinus Strobus. 



54-55. Stages in the first division of the microspore-cell ; the spindle 

 sharply pointed on the ventral side, broad on the dorsal side. X 810. 

 Pinus Strobus. June 7, 1898. 



56. Telophase in the first division of the microspore. X Sio. Pitius 

 Strobus. 



57. The resting stage following the first division of the microspore. 

 X 810. Pinus Strobus. 



58. The same as Fig. 57, but showing an exceptionally large prothal- 

 lial cell. X 8io- Pinus Strobus. 



59-60. Spireme-stage and early telophase in the division to cut off the 

 second prothallial cell. X^io. Pinus Strobus. 



61. The germinated microspore at the close of the second division, show- 

 ing the first prothallial cell already in an advanced stage of disintegra- 

 tion. X 810. Pi7ius Strobus. 



62-63. Stages in the third division of the microspore, showing the rapid 

 and almost complete obliteration of the first and second prothallial 

 cells. Both prothallial cells are cut off from the apical cell by definite 

 walls. X Sio. Pinus Strobus. 



( 164) 



