130 



COLLEGE BOTANY 



less strands appear and take the f onn of a spindle which is com- 

 posed of two parts, the outer and inner series. 



The lines of the spindle have very much the same appearance 

 as the meridian lines on a globe. The chromosomes become more 

 or less V-shaped and collect at the equator with their points 

 directed towards the center. Each chromosome divides longi- 

 tudinally into two apparently equal V-shaped structures 

 (Fig. 90). 



This gives double the number of chromosomes, one-half of 

 which travel towards one pole and the other half towards the 



FIG. 90. Stages in the mitotic divisions of the cell. 



other. These two groups of chromosomes become the nuclei of 

 the two new or daughter cells. The strands of the inner spindle 

 become thickened at the equator and develop into a wall sep- 

 arating the two new cells. 



Certain ones of the new cells retain their meristematic char- 

 acter and divide again, while other cells enlarge and develop into 

 the elementary tissues which we have studied in Chapter II. 



The preceding discussion is very general. There are many 

 modifications, but only a few can be discussed in a work of this 

 kind. Nuclear divisions without the formation of cell walls 

 sometimes occur in the formation of the endosperm in the em-, 

 bryo sacs of some plants. 



In some cases, especially in old cells, the division is direct 

 instead of being preceded by the mitotic division of the nucleus. 



