No. 466.] STUDIES ON PLANT CELL.— VIII. 729 
have a distinct organization which holds throughout the life his- 
tory. The form of the chromosomes certainly does change with 
different periods of the cell’s history especially within the rest- 
ing nucleus and yet the centers of chromosome activity may 
always be present to organize the chromatin into a new set of 
elements for the next mitosis. It is perhaps difficult to believe 
that the chromatin granules (chromomeres) find their way back 
to the same chromosome with the prophase of each mitosis but 
the existence of chromosome centers may be readily conceived 
within the resting nucleus which would hold the number of chro- 
mosomes true to the cell’s history. 
With respect to the nucleolus there is abundant evidence that 
the structure is not a permanent organ of the cell. When con- 
taining chromatin, the nucleolus is found in its characteristic 
globular state only during the resting condition of the nucleus. 
Its chromatic substance passes into the chromosomes at pro- 
phase of mitosis and the nucleolus generally disappears before 
metaphase. Or if any substance is left after the chromosomes 
are formed the remaining structure either gradually dissolves or 
is thrust forth bodily into the cytoplasm surrounding the mitotic 
figure where it disappears sooner or later. The nucleolus in 
higher types of mitosis never divides to pass on with the chro- 
mosomes to the daughter nuclei, but such a history is reported 
in the yeast cell. If the nucleolus has any function in heredity, 
as has been claimed (Dixon, ’99), such function must relate to 
the chromosomes which contribute to its substance or derive 
material from it. Besides the nucleoli which are composed 
wholly or largely of chromatin, there are also those which seem 
to have little if any relation to the chromosomes. Such are 
well known in the spore mother-cells of higher plants and no 
investigator has been able to connect these with the formation 
of chromosomes as Wager (:04) has been able to do in the root 
tip. It was upon nucleoli of this class that Strasburger founded 
his theory that the structure was a mass of reserve material 
utilized by the kinoplasm during mitosis in the process of spindle 
formation. Such nucleoli generally fade away during the pro- 
phase of mitosis and either entirely disappear or the remaining 
substance is thrust out into the cytoplasm where it may some- 
