Marquette, Banifestations of polarity in plant eella which usw. 293 



accummulation in the intervals between successive divisions if it 

 were not for the fact that here and there a cell is found which 

 is well supplied with starch in the late prophases or anaphases. 



It is possible that such cells possessed a superabundance of starch 

 so that although a part was used during mitosis a large amount 

 still remained, but as far as my observations go at present nothing 

 tan be said about this with certainty. 



It should be mentioned, too, that now and then one or several 

 starch grains are found lying outside of the polar structures in 

 the cytoplasm. These are isolated cases and seem to have no par- 

 ticiliar significance. 



The kidney shape assumed by the daughter nuclei at the time 

 of their formation persists for a considerable period. Frequently 

 it is still present when the new nuclear naembrane has been 

 completely formed and the chromatin quite uniformly distributed 

 through the nuclear space. As is well known, the nuclei of animal 

 cells frequently show during the telophases and even later a marked 

 indentation on their polar siele; in this indentation or just opposite 

 it the central body lies. This relation is duplicated in the cells 

 of the young leaves of Isoetes only that in this case the position 

 of the central bodies is oecupied by the polar starch masses. 

 Usually they lie closely pressed to the nucleus completely filling 

 its indentation. The cell represented in figure 7 has the upper polar 

 strueture developed just as well as the lower only the greater part of 

 it lies in the next section. 



Cell division takes place aecording to the method characteristic 

 of the higher plants. A well developed spindle is formed, wliich. 

 as it spreads out more and more laterally, is distinctly fibrous only 

 at the periphery, its interior already shows the strueture which 

 the cytoplasm of the so-called „resting" cell presents. The polar 

 structures which tili now had the shape of a more or less flattened 

 and irregulär sphere become more elongated and frequently press 

 deeply into the nucleus. The nucleus has been increasing in size 

 all this time and the indentation in it may be due either to its 

 growing up around the polar strueture, or to an active pressing 

 into it on the part of the polar strueture. With this the cell has 

 passed once more into the typical resting condition. Before entering 

 into a discussion of the more general bearings of the observations 

 just described upon the problems of nuclear and cell-division it will 

 be well to see to what extent structures similar to the polar 

 structures of Isoetes oeeur in other plants. 



As early as 1839 Von Mohl 1 ) described for the spore-mother- 

 cells of Anthoceros a green colored, starch-containing body 

 (chromatophore) lying at one side of the nucleus. This chroma- 

 tophore divides in the middle, and then each half again divides 

 so that there are four of them placed about the nucleus at about 



1 ) Von Mohl, H: Über die Eutwickelung der Spuren von Anthoceros 

 laevis. (Verm. Schrftn. p. 84.) 



Beihefte Bot. Central!)!. Bd. XXI. Abt. I. Heft :-5. 20 



