16 INTRODUCTION. 
The bipolarity of the multipolar spindle now gradually manifests 
itself, and the multipolar structure rapidly becomes a typical bipolar 
spindle in which the chromosomes are arranged in the equatorial plate. 
Io 
ls 
DR oy 
Fic. 7.—Heterotypic mitosis in pollen mother-cell (Z. #zartagon). Development of spindle continued. 
E, the weft of spindle fibers forms a multipolar complex, 
F, a multipolar complex in which bipolarity has begun to manifest itself; the weaker poles seem to be 
drawn in or together. 
G, bipolarity is established and chromosomes more regularly arranged in equator. 
H, mature spindle, showing only 3 of the 12 chromosomes; chromosomes fastened endwise to spindle. 
This transformation is probably brought about by certain of the larger 
poles converging toward a common area or point, while others are 
drawn in (Fig. 7, G). The mature spindle is either truncated at the 
poles (sometimes broadly so) or pointed, and the chromosomes are 
