Division in the Root of Vicia Faba. 179 



stage, and during this stage, it is the important chromatin 

 centre. During division it becomes transformed into the 

 chromosomes. The nuclear thread formed in the earhest 

 stages of division merely serves as a path along which the 

 nucleolus passes its chromatin. When the nucleus divides, 

 it is necessary that its properties shall be distributed equally to 

 the two resulting nuclei. This is accomplished by the split- 

 ting of the chromosomes ; the daughter chromosomes of each 

 of the nuclei formed are equal in value. 



Within recent years, the greatest importance has been 

 attributed to the chromosomes as the sole bearers of the 

 hereditary substance. It is true that the chromosomes are 

 bearers of the hereditary substance. But no more importance 

 should be assigned to these than is assigned to the nucleolus. 

 The chromatin in the chromosomes contains the active heredi- 

 tary substance, but in the resting stage, this hereditary sub- 

 stance is largely distributed or held in the nucleolus. The 

 inactive chromatin elements of which the nucleolus is composed 

 are the ones which become the active chromatin or hereditary 

 substance of the chromosomes. Therefore we must assign to 

 the nucleolus as well as to the chromosomes the function of 

 containing hereditary substance. The only difference is that 

 these hereditary elements are inactive in the nucleolus, whilst 

 in the chromosomes, they are in an active state. 



My best thanks are due to Dr. Mary Schively, who kindly 

 reproduced the figures of the accompanying plate from my 

 stained preparations. 



