'62 Olive, ^litotic division of tlic iniclei ol" ilio ( Vanophyceae. 



proper staining witli iroii haematoxylin, tliat tlie cliromosomes 

 in tig. 17, e. g., are globiilar or nearly so, and that they are 

 quite separate and distinct l'rom the acliromatic portion, The 

 nchromatin in tliis instante is npparently most dense in the 

 inimediate proximity of the ehroniosonies. (-p-p, 21, 22.) 



(3) Number of chromosomes constant. One of the 

 strongest evidences that a mitotic division must take -place is 

 tliat the nnniber of chromosomes is constant for the same 

 sj)ecies. In Glorocapsa and Nosfoc. there are 8. In two of the 

 species of O.scUlaior'ia studied , in PJionmdium and Calothrix, 

 there are 16; ^vllik^ in Osci/laforia princeps and in 0. Frodicliia^ 

 there are probably 32. In side view, the longitudinal sections 

 of cells with 16 chromosomes show usually 3 or 4; those with 

 32, as many as 8. (p. 11.) 



(•i) Longitudinal fission of chromosomes. This con- 

 stitutes the most necessary accompaniment of mitotic division. 

 In the case of Glococapsa, it is plainly evident that a longitudinal 

 fission of the spireme thread is taking place, or has akeady 

 been accomphshed, in iigs. 67, 70, 71, 74, 75. It is equally 

 evident that an equatorial fission of the central body is occur- 

 ring in figs. 6, 8, 10, 13, 34, 37. 80, etc. Since we find in such 

 cases as figs. 8 and 13, indisputable evidence of the doubling 

 of the number of chromosomes, one must conclude that each 

 individual chromatin granule is divided longitudinally in a plane 

 parallel to the cross partitions. The fission of all the chromo- 

 somes in a Single nucleus probably does not take place simul- 

 taneously, for it appears to begin at the two extremities or 

 outer edges of the spireme and thence to advance to the middle, 

 in the same manner as the progressive fission of the central 

 body (figs. 8, 13, 74, 75). (pp. 23, 29.) 



The fact, observed by many investigators , that the central 

 bodies of the vegetative cells of the Cyanophy(>eae have no 

 nuclear membrane is due, in the opinion of the writer, to thoir 

 continuous mitotic activity. It is probable that, if the nuclei 

 could be made to enter a resting condition, they would then 

 form both karyolymph and membrane, This probability is 

 rendered the more credible by certain facts: first, that the nuclei 

 of Oscillatorla^ even in active filaments, occasionally seem to 

 show nuclear sap and a poorly defined limiting membrane. Se- 

 condly, by the fact, observed by Wager, that the nuclei in 

 young cells are offen limited toward the cytoplasm by a „vacuolar 

 membrane" ; and finally, because in spores and heterocysts we 

 find nuclei in the usual resting condition. 



It will be of interest, then, if the vegetative ceUs of the 

 Cyanophyceae are in a state of continuous mitotic activity, to 

 determine how near to a resting condition their nuclei come. 

 In Gloeocapsa, in the very youngest cells (figs. 62, 64, 69, 76), 

 one may see, more or less clearly defined, the eight irregularly 

 disposed chromatin granulös, imbedded in an acliromatic sub- 

 stance. Probably the next step in the karyokinetic changes is 



