PLATE VII. 



Fig. 73. A vertical section through the upper part of an ovule shortly before fer- 

 tilization ; reconstructed from three adjacent sections of the series; o, 

 last vestige of spongy tissue. X ^2. Pinus Strobus, June 15, 1898. 



74. Pollen-grain from the nucellus of Fig. 73. The antheridial cell is still 

 undivided. X 472. 



75. A vertical section through the extreme upper portion of an ovule soon 

 after pollination, showing the uppermost part of the nucellar cap, and a 

 pollen-grain in the first stages of germination ; p.c, pollen-chamber. 

 X472. Pinus Strobus. June 13, 1S9S. 



76. A pollen-grain soon after germination. The tube-nucleus is moving 

 into the pollen-tube. X 472. Phius Strobus. June 24, 1S9S. 



77. A pollen-grain after the tube-nucleus has passed into the pollen-tube. 

 X472. Pinus Strobus. July 15, 1898. 



78. Spireme stage in the division of the antheridial cell. y(^i,^oo. 

 Pinus rigida. April 27, 1898. 



79-80. Stages in the division of the antheridial cell. Xi'400' Pinus 

 Strobus. August 4, 1898. 



81. A poUeh-grain after the antheridial cell has divided. X 472- Pinus 

 Strobus. August 4, 1898. 



82. The same at a later date, showing a slight increase in the size of the 

 generative cell. X472. Pinus Strobus. October 7, 1898. 



( 168 ) 



