tort} LUTMAN—CLOSTERIUM 423 
preceding night. In these species of Closterium, however, they are 
further to be looked upon as being a preparation for a division 
of the nucleus and cell the following night, providing it has been 
Successful in storing enough food material to make the process 
possible. If the individual is not able to synthesize enough starch, 
the nuclear and cell division is not carried out, and the two- 
parted chromatophore is retained indefinitely. In these species 
of Closterium, cell and nuclear division is at least a two-night pro- 
cess: the first night the chromatophore divides, cutting in two the 
greater part of the cytoplasm, but still retaining a connection 
between the two parts by means of the granular peripheral layer; 
the second night the nucleus may divide and the new wall separate 
the cytoplasmic halves entirely by cutting through the granular 
ayer. 
The question of the relation of the nucleolus to the chromatin, 
especially in the division stages of that part of the nucleus, is still 
an unsettled one both for plants and animals, and it is one that 
comes sharply into the foreground in this study of the division of 
the nucleus of Closterium. It would seem probable that, if the 
globular and nearly homogeneous nucleolus of Spirogyra contains 
the entire mass of chromatin in the form of a condensed spireme 
thread, as Moxy (32), Mirzkewrrcu (31), KARSTEN (25), and 
others have found, this much more strikingly compound nucleolus 
of Closterium, arranged occasionally so as to resemble a spireme, 
should represent the chromosomes aggregated into a central clump. 
That the chromosomes are really formed from the nuclear reticu- 
lum in Closterium is certainly very decisive as to their morpho- 
logical independence. The spireme formed outside the compound 
nucleolus seems indeed to be poor in chromatin, and the probability 
of the nucleolar material being used in the formation of the spireme 
fannot be denied. This, however, is also in some degree the case 
m the nuclei of the higher plants, and we are bound to conclude 
that the relations of nucleolus and chromosomes are probably the 
Same in all nuclei, in spite of the much discussed evidence for a 
chromatin nucleolus in the Conjugatae. 
If the spireme really thickens by the absorption of liquid 
material derived from the nucleolus, this can hardly be regarded, 
