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 earliest 
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 so/e 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. 
