12 INTRODUCTION. 
contains a row of larger granules or disks (the Chromatinscheiben of 
the German literature) of a tolerably uniform size, becomes a hollow 
spirem whose irregular turns traverse the nuclear cavity (Fig. 5, C). 
The chromatin disks have usually a jagged or erosed outline, which 
shows that each disk is composed of smaller granules. The chromatin 
disks, first carefully described by Strasburger (’82), vary much among 
themselves in size, and do not always have the same orientation in the 
linin thread. This fact, together with the twisting of the thread upon 
its axis, which is a mechanical necessity, gives the impression of a 
spirem composed of very irregular granules. This is especially notice- 
Fic. 5.—Pollen mother-cell and early prophase of first or heterotypic mitosis. A, F, Podophylium 
peltatum. B-E, filelleborus. Satidus. 
A, typical pollen mother-cell, with nucleus in resting stage, and while the cells are in tissue connection. 
B, linin net with numerous small chromatin granules. 
C, spirem in which chromatin disks are of uniform size. 
D, pieces of chromatin spirem more highly magnified; «, before longitudinal splitting; 4, after longi- 
tudinal] splitting, 
E, the spirem has split longitudinally ; daughter segments show a tendency to separate. 
F, the chromatin spirem has segmented transversely into chromosomes; daughter segments twisted 
about each other, (All figures represent sections.) 
able immediately after the longitudinal splitting of the chromatin 
granules. At this stage the most careful staining is necessary to bring 
out the chromatin disks clearly, since the linin retains the stain with 
greater avidity, thereby concealing the former. If the nuclear thread 
be too densely stained, it will appear more or less homogeneous, in 
which case the chromatin disks manifest themselves as a succession 
of enlargements whose granular character is concealed. The chro- 
matin thread consists, therefore, not of a succession of chromatin disks 
