22 PROTOPLASM AND PLANT CELLS 



matin granules spreading themselves out along the thread 

 until it is of even thickness. The thread rapidly shortens 

 and thickens, eventually becoming a thick, more or less 

 distinctly spirally arranged thread (spirem stage). At 

 the same time the nucleolus has been growing smaller or 

 less distinct and soon disappears entirely. In the spirem 

 thread there often becomes visible at this stage a split for 

 its whole length. However, it does not separate along 

 this split as yet. In the mean time outside the nucleus 

 there begin to appear in the cytoplasm immediately 

 surrounding the centrosomes fine lines, or fibrillae (of 

 kinoplasm) , which appear to center at the centrosome and 

 extend from it in all directions but especially toward the 

 nucleus. In the plants which have no centrosomes there 

 appear near the poles of the nucleus tangled masses of 

 fine fibrillae which in some cases form a sort of cap at each 

 pole or even may entirely surround the nucleus. From 

 this tangled mass the fibrillae gradually untangle them- 

 selves somewhat and finally lie in the form of a cone at 

 each pole, with the apex away from the nucleus. In the 

 forms with centrosomes one of the latter lies at each apex, 

 often surrounded by radiating fibrillae which may reach 

 out even to the cell wall. Where the mass of fibrillae 

 comes in contact with the nucleus the nuclear membrane 

 disappears and soon after vanishes at all other points 

 also. The fibrillae push into the nuclear cavity. In the 

 meanwhile the spirem thread breaks transversely into a 

 number of segments called chromosomes, the number 

 being constant for all vegetative nuclei of a given species 

 of plant. Two sets of kinoplasmic fibrillae can now be 

 recognized. Some push through the nuclear cavity until 

 they meet and unite with similar ones from the other pole, 

 forming a spindle-shaped structure commonly spoken of 

 as the nuclear spindle. Other sets of fibrillae push toward 



