Olive, Mitotic division of tlie nuclei of the Cyanopliyceae. 
25 
in tlie fonr cells at b and c, although division of tlie cell lias 
evidently been just acconiplislied, we can see evidences in tlie 
double row of chromatin granules in each tliat mitotic division 
lias already begun, if not, indeed, already completed. Figs. 7, 
8. 10, 13, 14, and 17 also show tliat division lias advanced 
fartlier in certain cells than in tlieir immediate neiglibors. Fig. 13 
is particularly interesting in this connection in tliat tlie two con- 
tiguous daugliter lialves liave begun to divide, whereas tlie two 
nuclear lialves uppermost and lowerniost in tlie drawing do not 
yet sliow any evidence of fission. It is possible tliat tlie distri- 
bution of food supply lias something to do in causing tliese 
rliytlnnic centers of division. 
Tlie nuclear membrane. 
It is truly remarkable tliat, in tlie actively vegetating fila- 
ments of tlie Cyanopliyceae, tlie nuclei appear to be continually 
dividing, without entering upon a resting condition. At least, 
none of tlie many investigators who liave studied tlie group liave 
been able tlius far to find a resting state in wliicli the nucleus 
forms a inenibrane and nuclear vacuole as it does in the nuclei 
of the higher plants. The absence of a nuclear membrane has 
been claimed by many to be evidence against the nuclear nature 
of tlie central body; but, in the opinion of the writer, this mem- 
brane does not carry with it such weight, since its absence in 
this instance is probably due to ä lack of a resting condition 
prolonged enough in which to produce it. I believe, in fact, 
tliat if we could make the cells of Oscillatoria rest from tlieir 
activities sufficiently long, the nuclear membrane and sap cavity, 
as well as other attributes of the resting nucleus, would be formed. 
Indeed, as will be explained later, this membrane is actually 
formed in spores and lieterocysts, and possibly even sometimes 
in active vegetative cells. 
H ieronymus (92) tliought tliat tlie central body is „open", 
tliat is, not separated from the eytoplasm by a membrane; hence, 
he called it an „open cell nucleus“. Palla (93), on the other 
hand, who tliought tliat tlie whole central portion was homoge- 
neous, says that there is always a colorless membrane between 
the central body and the peripheral chromatophore. He gl er 
(01) asserts tliat such a membrane is not present ; while Wäger 
(03) says tliat, although there is no nuclear membrane, in young 
cells the central body is often limited towards the eytoplasm by 
a „vacuolar membrane“, which may possibly represent at least 
a rudimentary nuclear membrane“ (p. 407). Kohl (03) remarks 
tliat there is wanting in these plants a „deutlich färbbare Kern- 
membran“ (p. 184). Lawson (03), in an article on the nuclear 
membrane, could find in the Cyanopliyceae and Bacteria neither 
membrane nor karyolymph. It is stränge tliat this writer has 
overlooked the fact that Strasburger (82), over twenty years 
ago, anticipated four out of his six conclusions. In giving some 
of the results of his work with the resting nucleus, Strasburger 
