No. 450.] STUDIES ON THE PLANT CELL. 



443 



very difficult to follow in these forms and is not fully known, hut 

 multipolar conditions are reported which later chan-c into bipolar 



While the spindle is being organized by kinoi)lastiHi- arlivitics 

 outside of the nucleus, some events occur within whii h loiin a 

 very important part of the prophases of mitosis. I'he luun 

 material, which in the resting nucleus -eiierallv has the 1 01111 of 

 a net, becomes organized into a much Kx.pcd rihhon. cilled the 

 spirem thread. The chromatin material -athei s alon- the spirem 

 thread as deeply staining globular bodies. These split into halws 

 in the direction parallel with the a.\is of the spirem thread, and 

 the two sets of chromatic bodies lie in two rows along the ed-c 

 of the ribbon, which shortens as it grows older, l-'inally tiie 

 spirem thread divides transversely into a dehnite number of seg- 

 ments, and these are the chromosomes. The chromosome are 

 generally fully formed at the time when the sjjindle fibers enter 

 the nuclear cavity, and they are readily moved as the librilhe 

 develop the spindle. Some of the fibers become attached to the 

 chromosomes, carrying them to the equatorial region of the 

 spindle to form the structure called the nuclear plate, which 

 always indicates the approach of metaphase. 



As the spirem thread matures the amount of chromatin is 

 greatly increased, so that the separate globules run together and 

 cannot be distinguished in the chromosome which is homogeneous 

 in structure. Chromatin has its greatest staining power at this 

 period. Whether linin is closely related to chromatin in compo- 

 sition and is actually changed into that substance, or whether it 

 dissolves and contributes its material to the growth of the spin- 

 dle, is a problem of some importance as yet unsolved. It is 

 possible that the nucleolus may furnish material tor the chromo- 

 somes, and some nucleolar like bodies are known to be chi-omatic 

 in character, but it does not seem to be established that any <jf 

 these are genetically related to an unquestioned nucleolus in any 

 plant form. 



Important changes come over the nucleolus coincident with the 

 development of the chromosomes. The structure frequently 

 gives signs of internal modifications early in prophase and before 

 the development of the spindle. It may gradually fade away or 



