INTRODUCTION. 



ing shorter and thicker, and frequently no trace of the longitudinal 

 splitting can be recognized. There is thus formed the loose, hollow 



FIG. 6. Prophase and early stages in development of spindle in\ heterotypic mitosis of pollen mother- 

 cell. A, B, Lilium candidum. C, D, L. martagon. 



A, the kinoplasmic spindle fibers arranged radially about the nucleus, large nucleolus present, and the 



chromosomes, each consisting of two rather thick segments twisted about each other, lie along the 

 nuclear membrane or scattered through nuclear cavity. 



B, same developmental stage as A ; here the kinoplasmic fibers are disposed partly radially and partly 



in form of a weft lying in cytoplasm midway between nucleus and cell-wall. 



C, the spindle fibers are encroaching upon the nucleus, forming a weft about it ; the nuclear membrane 



as such has nearly disappeared ; it seems to have been converted into fibers. 



D, multipolar spindle complex, in which the chromosomes are irregularly distributed. 



spirem, which segments by transverse division into the chromo- 

 somes. 



