PLATE I. 



FIG. i. Two cells of the primitive archesporium showing the winter condition 

 of this tissue. X 1,400. Pinus austriaca. December 20, 1897. 



2. A cell from the primitive archesporium in the early spring. Many of 

 the cells of the archesporium are undergoing division at this time. 

 X 1,400. Pinus austriaca. March 14, 1898. 



3. A cell of the definitive archesporium, the microspore-mother cell, just 

 prior to the inception of its division. X 1,400. Pinus austriaca. April 

 27, 1898. 



4. The same as fig. 3. X 1,400. Pinus Strobus. May 24, 1898. 



5. The microspore-mother-cell approaching synapsis before a definite 

 spireme has been formed. X 1,400. Pinus austriaca. April 28, 1898. 



6. The same as fig. 5. X 1,400. Pinus Strobus. May 24, 1898. 



7. Synapsis. X 1,400. Pinus Strobus. May 24, 1898. 



8. Recovery from synapsis, showing a continuous spireme. X 1,400. 

 Pinus Strobus, May 24, 1898. Material showing figs. 4 and 6 was col- 

 lected from a different tree than that showing figs. 7 and 8, and the 

 microspore-mother-cells were in a slightly different stage of division. 



9. Complete recovery from synapsis. Chromatin in irregular granules, 

 on a broad linin band. X 1,400. Pinus Strobus. 



10. The longitudinal splitting and transverse segmentation of the spireme. 

 Chromatin still distributed in irregular granules. X 1,400. Pinus 

 Strobus. 



11. Longitudinal splitting completed, but the sister segments do not become 

 entirely disunited. Nucleoli still apparent. X I >4OO. Pinus Strobus. 



12. a-e. Portion through the edge of a nucleus showing the twisting 

 of the" chromatic segments after longitudinal splitting. In most in- 

 stances these are not entire segments but portions that have been 

 severed by the microtome knife. The entire segments are very long 

 and coiled at this time. X 1,400. Pinus Strobus. 



13. Early stage in the condensation and fusion of the longitudinally divided 

 spireme. Threads anastomosing in region of nucleoli. X 1,400. 

 Pinus Strobus. 



(156) 



