HISTOLOGY 



FIG. 29. Hyacinth root-tip cell with spireme 

 entire but ready to break into the chromo- 

 somes. Spindle formed. Spireme appears to 

 be divided owing to process of sectioning. 



gone, the nucleolus is gone, and the spireme is compressed into an oval 



to round mass, lying at right angles 

 to the spindle and the plane of the 

 equator, halfway from pole to 

 pole. 



This round mass, which is a flat 

 disk in the dividing cells of some 

 other plants and animals, is still 

 the continuous spireme noted be- 

 fore; in its later stages several 

 breaks may be seen with the loose 

 ends springing up from the main 

 body. The spindle fibers, which 

 are now developed into longer 

 cones, touch the equatorial mass 

 of chromatin and appear to have 

 established a continuity through 

 its meshes, so that a fiber starting 

 at one pole runs without break 

 through the spireme to the oppo- 

 site pole. The breaks observed in the spireme (not shown in Fig. 29) 

 increase until the whole spireme 

 has been divided into 



a number 

 of equal parts. There are twelve 

 in the case of the hyacinth root- 

 tip. These portions of the spireme, 

 known as chromosomes, quickly 

 move into one of the most com- 

 monly seen figures as pictured in 

 Figure 30. Here the chromosomes 

 are scattered as by the snap and 

 momentum of their breaking, and 

 yet two facts must be noticed; 

 some part of each one is still re- 

 tained in the equatorial plane of 

 the spindle, and such parts of the 

 chromosomes as have moved from 

 this plane lie usually among and 

 parallel to the fibers of the spindle. 

 The wandering portion usually 

 consists of a free end of a chromo- 

 some. 





FlG. 30. Hyacinth root-tip cell. Spireme 

 newly broken into the chromosomes. 



Ordinarily the wandering ends are found on each side of the equa- 



