[ 707 ] 



XL. 



ON THE CHROMOSOMES OF LILIUM LOT^GIELOETJM. By 

 H. H. DIXOjS", B.A., Assistant to the Professor of Botany, 

 Trinity College, Dublin. 



(Plate XXIII.) ~ 



[cOMMUlflCAXED Br DE. E. P. WEIGHT.] 



[Eead November 11, 1895.] 



The following is a short account of some observations on the nuclei of 

 Lilium longijlorum, which were made with the special object of deter- 

 mining accurately the number of the chromosomes formed by the 

 nuclear thread in mitosis both in the sexual and asexual cells. 



The preparations were obtained from material fixed in alcohol, the 

 sections being made by a microtome using the ordinary paraffin- 

 embedding process [vide Zimmerman, Bot. Mikrotechnik). No fixative 

 was used, but the sections in paraffin were spread on the slide floating 

 in water and after the evaporation of the latter they adhered to the 

 glass and kept their position for succeeding manipulation. Staining 

 was carried out either en Hoc by immersing the small portions of the 

 plant to be examined in dilute stain for several days previous to 

 embedding, or after the sections were cut and fixed on the slide. 

 With Delafield's Hsematoxylin, the first method gave the clearest 

 nuclear staining, although by the second scarcely inferior results are 

 obtainable, when great care is taken to free the sections thorou.shly 

 from all traces of paraffin, xylol, and alcohol before putting them 

 into the dilute stain. In the preparations obtained by staining en bloc 

 the chromatin elements only of the nuclei are stained ; but if staining 

 is carried out after sectioning, the cell-walls are stained, 'ihe latter, 

 when the sections are thin, do not obscure the structure of the nuclei. 

 The chromosomes of the dividing nuclei of the vegetative cells are 

 usually most easily counted in series of sections, each of which is 

 5/x or 10 /A thick. Often, however, when dealing with the large 

 nuclei in the pollen-sac or embryo-sac, it is useful to cut some 

 sections 15 or 20 /x, in thickness. 



