Olive. Mitotic division of tlie uuclei of tlie Cyaiiopliyceae. 25 



in the four cells at h and r, althougli division of tlie cell lias 

 evidently been just acconiplislied, we can see evidences in tlie 

 double row of cliromatin granules in eacli tliat mitotic division 

 lias already beguii, if not, indeed, already completed. Figs. 7, 

 8, 10, 13, 14, and 17 also sliow that division lias advanced 

 farther in certain cells tliaii in their immediato neiglibors. Fig. 13 

 is particularly intercsting in tliis connection in tliat the two con- 

 tiguous daugliter halves have begun to divide, whereas tlie two 

 nuclear lialves uppermost and lowerniost in tlie drawing do not 

 yet show any evidence of iission. It is possible tliat tlie distri- 

 bution of food supply lias sometliing to do in causing these 

 rliythmic centers of division. 



The nuclear membraue. 



It is truly remarkable tkat, in tlie actively vegetating fila- 

 ments of tlie Cyaiiopliyceae, the nuclei appear to be contiiiually 

 dividing, without entering upon a resting condition. At lea.st, 

 none of the niany investigators who have studied the group have 

 been able tlius far to find a resting state in whicli the nucleus 

 forms a membrane and nuclear vacuole as it does in the nuclei 

 of the higher plants. The absence of a nuclear membrane lias 

 been claimed by niany to be evidence against the nuclear nature 

 of the central body; but, in the opinion of the writer, tliis mem- 

 brane does not carry witli it such weigiit, siiice its absence in 

 this instance is probably due to a lack of a resting condition 

 prolonged enougli in which to produce it. I believe, in fact, 

 that if we could niake the cells of OsciUatoria rest from their 

 activities sufhcieiitly long, the nuclear membrane and sap cavity, 

 as well as otlier attributes of the resting nucleus, would be formed. 

 Indeed, as will be explained later, this membrane is actually 

 formed in spores and heterocysts, and possibly even sometimes 

 in active vegetative cells. 



Hieronymus (92) thought that the central body is ,,open", 

 that is, not separated from the cytoplasm by a membrane; hence, 

 he called it an „open cell nucleus". Palla (93), on the otlier 

 hand, who thought that the wliole central portion was honioge- 

 neous, says that there is always a colorless membrane between 

 the central body and the peripheral chromatophoro. Hegler 

 (Ol) asserts that such a membrane is not present; wliile Wager 

 (03) says that, althougli there is no nuclear membrane, in young 

 cells the central body is offen limited towards the cytoplasm by 

 a „vacuolar membrane", which niay possibly represent at least 

 a rudimontary nuclear memljrane" (p. 407). Kohl (03) remarks 

 that 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 Cyanopliyceao and Bacteria neither 

 menil)rane nor karyolymph. It is stränge that this writer lias 

 overlooked the facit tliat Strasburger (82), over twenty years 

 ago, anticipated four out of his six conclusions. In giving some 

 of the results of his work willi the resting nucleus. Strasburger 



