5 T 4 
Notes. 
between them, the whole being surrounded by a very thin membrane 
which is only visible at the two ends. This is the structure which we 
may call a nucleus. It is surrounded by a space containing a substance 
which is only slightly stainable, and this again is surrounded by a 
deeply stained membrane, outside which is the slightly stained gela- 
tinous envelope. Previously to its division the cell elongates; the 
nucleus also elongates and contracts slightly about the middle of its 
length. A dumb-bell shaped structure is thus obtained. The two 
nuclear rods divide completely to form two groups containing two 
rods each, which remain connected together for some time by the 
less deeply stained portion of the nucleus. The constriction becomes 
more and more pronounced until finally the two halves of the nucleus 
are completely separated. The outer capsule or cell-wall has mean- 
while been also contracting towards the middle ; the contraction 
keeping pace with the division of the central mass. This contraction 
goes on until, at a certain stage, a delicate transverse partition appears 
dividing it into two, each half contains one of the halves of the 
original nucleus. Ultimately the two halves become completely 
separated and two new cells are formed. 
In the majority of cases the cells are completely separated before 
the division of the nucleus again begins, but in many instances the 
nuclear rods were seen to be dividing in cells which were still con- 
nected with each other. 
After a time the division of the cells takes place less rapidly and 
finally ceases altogether. The division of the nucleus becomes very 
irregular, and at the time when cell-division has ceased the nucleus 
has become broken up into granules which are distributed irregularly 
in the contents of the cell. 
This breaking up of the nucleus appears to be preliminary to the 
formation of spores, although the formation of these has not been 
satisfactorily observed. 
HAROLD WAGER, Leeds. 
ORIGIN OF POLYSTELY IN DICOTYLEDONS.— Nearly 
all flowering plants have a monostelic structure in stem and root ; that 
is to say, their conducting system forms a single central cylinder (stele), 
which consists of the xylem- and phloem-strands, and of the conjunc- 
tive parenchyma by which they are united and surrounded, the whole 
being enclosed by a general endodermis belonging to the cortical 
