PLATE XV. 



Fig. 156. Surface view of a bit of the prothallium showing two free nuclei and 

 the vacuolate protoplasm surrounding them. X 744- Pinus Strobus. 

 May 17, 1898. 



157. A radial section through the lower portion of an ovule showing pro- 

 thallium, spongy tissue, and normal nucellar tissue. X472- Pinus 

 Strobus. May 26, 1899. 



158. As fig. 157, except that the spongy tissue and the normal nucellar 

 tissue are separated by a double layer of cells, belonging to the nu- 

 cellus, which have lost their protoplasmic content but their walls have 

 not yet collapsed. X 472. Pinus Strobus. May 26, 1899. 



159. A bit of the prothallium in surface view showing the complex cytoplas- 

 mic figure characteristic of the late telophase in free nuclear division. 

 X472. Pinus austriaca. May 17, 1898. 



160. Surface view of a portion of a prothallium immediately after the or- 

 ganization of cell-walls separating the free nuclei. X 472- Pinus 

 Strobus. May 26, 1899. 



i6i. A bit of the prothallium as seen in radial section just after cell-walls 

 have arisen. The cells are open on their inner surfaces and the 

 nuclei remain near the open sides. X 394- Pinus austriaca. May 

 20, 1898. 



162. A prothallium still open at the center showing that true "alveoli" as 

 described by Sokolowa are not present; the archegonia rudiments at 

 the micropylar end ; the spongy tissues still prominent. X 62. Pinus 

 austriaca. May 24, 189S. 



163. A condition often found in the ovule. The macrospore-mother-cell 

 has failed to develop and the walls of the spongy tissue have thickened 

 and stain deeply. X 46. Pinus Strobus. 



164-166. Figures illustrating karyokinesis in the spongy tissue. The 

 method is typic with the number of chromosomes characteristic of the 

 sporophvte. X 810. Pinus Strobus. 



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