PLATE VI . 



Figs. 64-65. Mature pollen-grains ; in fig. 64 the remnants of the two prothal- 

 lial cells can be seen, while in fig. 65 all signs of the first cell have 

 disappeared. X^io* Pinus Sirobtis. June 9, 1898. 



66. Vertical section through an ovule immediately after pollination ; the 

 macrospore-mother-cell is very conspicuous ; the upper portion of the 

 free limb of the integument is shown to be three cells in thickness, 

 there is a slight concavity in the apex of the nucellus ; macrospore- 

 mother-cell {m.m.c), nucellar cap {nuc), micropyle {mic). X 46- 

 Pinus rigida. May 27, 1902. 



67. Vertical section through the upper part of an ovule showing pollen- 

 chamber ; the middle layer of cells in the upper part of the free limb 

 of the integument has elongated and closed the microcarpylar canal. 

 X 46. Pinus rigida. June i, 1902. 



68. A vertical section through the upper part of an ovule. The elongated 

 cells noted in fig. 67 have become divided by the formation of cross 

 walls into smaller cells. X 46. Pinus rigida. June 4, 1902. 



69. A vertical section through an ovule some days after pollination. Axial 

 row [a.r.). X 62. Pinus Strobus. June 17, 1S9S. 



70. A vertical section of an ovule showing the winter condition. X62. 

 Pinus Strobus. January 4, 1898. 



71. A vertical section of an ovule soon after the second period of growth 

 has begun. X62. Pifius Strobus. May 26, 1898. 



72. A vertical section through the upper part of an ovule at the time of the 

 division of the generative nucleus ; («ac.i), that portion of the nucellar 

 cap which was developed during the first period of activity; {nuc. 2), 

 that portion of the nucellar cap which constitutes the second year's 

 growth ; o, disintegrating spongy tissue. X 62. Pinus Strobus. 

 June 9, 1898. 



(166) 



