LIFE HISTORY OF PINUS 21 



formerly, and the nuclear reticulum takes the blue characteris- 

 tic of chromatin. In this condition, the contracted state known 

 as synapsis is entered upon. 



The First Nuclear Division of the Microspore-mother-cell. 

 As soon as a microspore-mother-cell has attained full size, cer- 

 tain changes in its nucleus indicate that the prophase of the first 

 division has been initiated. The reticulum gradually draws 

 together, its threads becoming thicker and the meshes smaller 

 (figs. 5 and 6). Contraction continues until the network forms 

 a compact mass at one side of the nucleus. During synapsis 

 the nucleoli may be entirely confined within the contracted 

 sphere or one or more may be partially extruded (fig. 7). Some 

 of the nucleoli still stain deeply with the gentian-violet, but 

 one or more usually take the plasma stain at this time and 

 appear as yellow, porous, or spongy bodies. The same appear- 

 ance has also been obtained with iron-has matoxylin followed by 

 orange G. 



In Pinus rigida no appearance at all comparable with that 

 known as synapsis is observed until April 21. In material pre- 

 served on this date a few nuclei in all anthers show the begin- 

 nings of contraction as illustrated for P. austriaca in fig. 5 and 

 P. Strobus in fig. 6. On April 30 the nucleus of every mother- 

 cell has reached the point of greatest condensation, its contents 

 forming a somewhat spherical, deeply-staining mass at one side 

 of the nuclear cavity fig. 7 illustrates this stage for P. Strobus. 

 On May 2 some of the nuclei still retain this structure while 

 others show various stages of recovery. Two days later, May 

 4, not a vestige of this condition remains, all the nuclei having 

 passed on to more advanced stages in the mitosis. These 

 dates have been given for Pinus rigida, but they would not 

 differ materially in the other species, except that in P. Strobus 

 corresponding phases in this division would occur about 3 weeks 

 later. 



Synapsis is not universally recognized as a normal step in the 

 heterotypical division. Guignard ('97), Mottier ('97), Schaffner 

 ('01), and others still look upon it as an artifact caused by im- 

 perfect fixation. On the other hand, Sargant ('97), Wiegand 

 ('99), Duggar('99 and 'oo), Ernst ('01), Rosenberg ('01) among 



