118 



and distilled water, placed on a clean slide. The pollen mother- 

 cells will be thus set free in the fluid, which fixes them instantly. 

 The preparation may now be examined with a low power to 

 see if the desired stages are present. If this is the case a drop of 

 staining fluid should be added and a cover-glass placed over the 

 preparation. I have obtained most beautiful results by using 

 gentian-violet. A little of a strong alcoholic solution of this 

 stain is diluted with several volumes of weak acetic acid, (about 

 one part acid to two of water), and a drop of the stain thus di- 

 luted is added to the preparation. As soon as the desired stain 

 is produced, which takes but a minute or two, the stain should 

 be carefully drawn oft" with blotting paper and pure water run 

 under the cover-glass. By this process all the details of division 

 may be easily followed, as the chromatin stains very deeply, 

 while the protoplasm remains almost colorless. Such prepara- 

 tions may be kept for some time in dilute glycerine but soon fade. 

 The isolated spore mother-cells are characterized by their 

 thick, irregular walls, which remain intact until the final divisions 

 are completed. The resting nucleus of the mother-cell is large, 

 and has a very distinct membrane. It shows an indistinctly fila- 

 mentous structure, and in Allimn has a large nucleolus at one 

 side which colors but little, and from its position is sometimes 

 known as "para-nuclcus." It is probable that the "seg- 

 ments " or chromatin filaments, which later become so distinct, 

 are even in the resting nucleus entirely disconnected, and not 

 confluent as was formerly supposed. In Podophyllum the nu- 

 cleolus is much less conspicuous, and early becomes indistin- 

 guishable. 



As the nucleus prepares for division it increases very much 

 in size, and the chromatin filaments become much more distinct, 

 appearing as a tangled coil of threads, nearly fillinoj the cavity of 

 the nucleus (PL CIII. Fig. 2). These threads do not color evenly, 

 but consist of two substances, one of which does not color at all, 

 and later is scarcely to be seen; the other (chromatin) staining 

 very intensely, and in the earlier stages of division showinj^ more 



or less distinctly as separate portions (microsomes). These later 

 seem to coalesce more or less completely, so that the segments of 

 the later division-stages stain uniformly and very Intensely. 



