288 Marquette, Manifestations of polarity in plant cells which usw. 



is still linely distributed through tlie nuclear cavity, at tlie edges 

 of tlie furrow, however, the granules are more elosely crowded 

 than elsewhere in the nucleus, a distribution such as would result 

 from the local indentation of a plastic vesicle which contains uni- 

 formly distributed particles. 



The starch body does not always press deeply into the resting 

 nucleus, sometimes it merely lies elosely against it without indenting 

 it. and in these cases when the starch body divides the two sepa- 

 rating haives merely niove along the surface of the nucleus. These 

 cases are rarer, however, than those in which the nucleus is furrowed 

 by the separating daughter starch bodies. 



After the starch body has conipletely divided into two, the 

 haives withdraw from each other until they lie at opposiie poles 

 of the elongated nucleus, close against its menibrane, at the same 

 time they change their shape or their position so that their long 

 axes now are at right angles to that of the nucleus (figs. 2 & 3). 

 Frequently at this stage the cytoplasm between the starch bodies 

 and tlie plasma menibrane is more vacuolated and clearer than 

 elsewhere in the cell. At about this time the first indications of 

 an approaching division become apparent in the nucleus itself. the 

 chromatm begins to collect into larger aggregations. Frequently 

 a more or less diagonal furrow which was formed by the starch 

 body pressing into the nucleus in the earlier stages is still to be 

 seen at this stage. (Fig. 3.) Up to this time the chromatm 

 appears in the flnely divided condition characteristic of resting 

 nuclei and it is piain that we have in these cells a long series 

 of visible changes preparatory to cell division before the appear- 

 ance of the chromatm gives any indication of the beginning of 

 the prophases; neither are there any fibers or rays visible in the 

 cytoplasm up to this time. 



As the chromatin passes into the spirem stage 1 ), the polar 

 struetures leave the nuclear menibrane. moving further apart from 

 each other in opposite directions until frequently they lie close to 

 the plasma-membrane. As they do so they become still more 

 flattened and irregulär in outline. This irregularity of outline is 

 worthy of note for it is a further indication that the polar strueture 

 is not a vacuole whose form is determined by surface tension. As 

 the polar struetures move away from the nucleus, the cytoplasm 

 between them and the plasma menibrane assumes a denser appear- 

 ance; if the amount of cytoplasm here present is small it has 

 this denser appearance throughout its extent. It almost looks as 

 if the polar struetures in moving away from the nucleus had 

 pushed the cytoplasm ahead of them and thus crowded its Clements 



r ) The formation of a continuous spirem has been questioned in recent years. 

 See Gregoire and Wygaerts who worked on Trillium. La Cellule (T. XXi. 

 p. 5. 1904, and J. Kowalski who worked on Salamander larvae in Gregoire^ 

 laboratory. La Cellule (T. XXI. p. 349.) In the young leaf-cells of Isoetes a< 

 continuous spirem seems to be formed. I hare not. however, devoted any 

 special attention to determine whether possibly there are breaks in the apparently 

 continuous spirem. 



