1904] MERRIMAN: VEGETATIVE CELL DIVISION 193 
the appearance of a vacuole, one of a series ina network. As the 
nucleus enters into a quiescent condition then, the spaces in the 
centers of the groups of tetrads become more marked, and 
the boundary lines of the chromatin granules more and more 
indefinite. 
The history of the chromatin shows that up to the time of the 
formation of the equatorial plate the whole process can be sum- 
marized as consisting of the growth, aggregation, and fusion of 
tetrads into chromosomes; whereas the period from the forma- 
tion of the equatorial plate to that of the daughter nuclei can be 
summarized as a process consisting of the disintegration of chro- 
mosomes into tetrads and the reduction of the latter in size. 
The times of the appearance and disappearance of tetrads then 
correspond. with those of appearance and disappearance of a 
definite arrangement of the chromatin, and this holds for the 
nuclei which are about to divide as well as for those which have 
just arisen from division. 
From the time when the double strands of granules are first 
evident until the spireme is conspicuous, there is an increasing 
stainability, condensation, and enlargement of the component 
granules. Jigs. g and 76 represent successive stages in the 
growth of the spireme thread before it has broken up into chro- 
mosomes. The linin connecting the coils is seen to persist; but 
the connecting bridges are reduced in number. 
These linin connections never completely disappear, although 
the quantity of linin varies with the stage of division. The linin 
strands which persist in the late spireme are more deeply stain- 
able than the earlier connecting bridges. This suggests that this 
reticulum may arise, concomitantly with the growth of the chro- 
matin, from the fusion of some of the earlier connections, while 
other connections are torn apart with the growth and consequent 
pulling apart of the coils. A cross-section of the spireme loop 
taken in early stages shows it to consist of four granules joined 
by the linin in the form of a square; a cross-section taken at 
Stages immediately preceding that of its maximum size shows 
that the granules have approached one another in their growth. 
Its structure is thus seen to be, not that of a homogeneous single 
