380 BULLETIN OF THE 



becoming " inhaltsarmer." Whether this transfer of substance is accom- 

 plished in the form of visible granules, in any way comparable with a 

 nuclear plate, seems doubtful from Strasburger's description ; but if his 

 studies were confined to alcoholic preparations, it would have been very 

 easy, even for so accomplished an observer, to have overlooked nuclear- 

 plate stages, which are always of comparatively short duration. I do 

 not, however, wish to express any opinion on this point, without the 

 personal observations necessary to an independent judgment. May it 

 not be, however, that TschistiakofF's ('75) statement — that the nuclei are 

 found much nearer the planes of division than are the clusters of starch 

 granules to which they correspond — is based upon the observation of 

 stages in the migration of a nuclear plate (his nucleus), which were not 

 seen by Strasburger *? The latter observer, it is true, states that the 

 nuclei lie at first in contact with the cluster of starch granules, and sub- 

 sequently move away from the latter. So far as T know, however, such 

 a migration away from an " Attractionscentrum " has not been observed 

 by others. 



In Strasburger's opinion the least modified methods of cell division 

 are such as prevail when the whole cell contents are granular proto- 

 plasm, and the nucleus is central. Here the nucleus plays an important 

 role (through the interzonal filaments) in the formation of the cell wall. 

 All other causes are, to a greater or less extent, modifications of this. 

 It is shown, further, that the share which the nucleus has in this process 

 may be gradually diminished, and for it may be substituted the activity 

 of the mural protoplasm. The formation of the cell partition may thus, 

 in place of being simultaneous, at length be brought about by the succes- 

 sive steps of an ingrowth from the mural protoplasm. The function of 

 the nucleus in cell division has thereby suffered a reduction, and an ulti- 

 mate condition is to be found in such cases as Cladophora,* where the 



* p. S. — ScHMiTZ ('79) has brought forward evidence to show that, contrary to 

 the opinion held by Strasburger, the bodies which he ('76, p. 87) saw in Cladophora, 

 and designated as " halbkugelige Anhaufungen kornigen Protoplasmas, " are really 

 cell nuclei. Schmitz has shown, among other things, that they behave like nuclei 

 when treated with reagents, and has followed them during division, in which, how- 

 ever, he has been able to gain only unsatisfactory evidence of a filamentous differen- 

 tiation. An elongation always takes place prior to division, and a diminution in the 

 intensity with which the body stains is at this time accompanied by a gradual mass- 

 ing of the nuclear substance at the two poles. The nuclear division is positively not 

 accompanied by a division of the protoplasm, so that from the uninuclear germ 

 there results first one and then a number of multinuclear cells. He corroborates 

 Strasburger in making the cell division, when it does occur, quite independent of 

 these nuclear structures. 



