128 



THE PHYSIOLOGY OF PI«|lBfTS 



The latter is a turbid, thickisli liquid, which afterwards becomes 

 clearer, and takes up certain stains less actively than the 

 framework, which consists of the nuclear plasma (nuclein, 

 chromatin). 



In Fig. 2 1 we see in (i) a nucleus in the young mother 

 cell of the stomate guard cell before its division ; in (2) we 

 recognise more distinctly the chromatin framework, which we 

 see in (3) is formed of pieces of a thread. These pieces of 

 the nuclear thread are arranged (in 4) in the median plane 

 of the cell in which the new wall is to be formed. 



They now form what is called the equatorial plate. The 



B"IG. 21.— NnoLEAR Division in a Guard Cell of Iris pumila (after Haberlaiidt). 



nuclear substance now divides itself into two, and one-half 

 proceeds to each pole of the cell ( 5 ), where it becomes arranged 

 to form one of the daughter nuclei (6—9). 



The movement of the various portions of the original 

 nuclear thread towards the centre, and the return of the 

 halves of these segments after division, takes place along a 

 number of threads which are formed in the protoplasm, and 

 are termed the spindle threads. These threads converge at 

 the two poles, but separate one from the other in the middle 

 of the cell (4-7)- By the time these threads make their appear- 

 ance, the former covering of the nucleus, nuclear membrane, 

 has disappeared, and the threads traverse the entire cell ; 



