228 The Microscope. 



whole better adapted for the study of the cell and cell-division 

 than dicotyledons, as the cells are usually larger and the nucleus 

 correspondingly so. Among the very best plants for the study 

 of the nucleus, especially in the cell are various species of Tra~ 

 descantia whose cells are uniformily large with large and distinct 

 nuclei. To follow the division in the living cell, the hairs at- 

 tached to the filaments of the stamens should be used. By 

 selecting young buds before the purple color is developed and 

 carefully removing the whole stamen with the attached hairs,, 

 specimens in all stages of division may be found. If they are 

 mounted in fresh water or a 3 per cent, solution of sugar, ther& 

 is little difficulty in seeing the whole process in the same cell, as- 

 the cells remain alive for 24 hours or more. 



In Tradescantia as in many other monocotyledons, the pollen 

 mother-cells ofi'er exceptionally good subjects for demonstration. 

 The wild-onion {Allium Canadense) is also excellent for this pur- 

 pose, and either one will enable us to get a good idea of the finer 

 structure of the nucleus as we find it in the higher plants. 



In studying the division of the pollen-spores, for quick dem- 

 onstration they may be fixed with acetic acid and stained with 

 gentain-violet. Such preparations are not permanent, but show 

 beautifully all the details of nuclear-division. 



The resting nucleus is separated from the surrounding proto- 

 plasm by a thin but very evident membrane, and is usually 

 globular or lenticular in form. As to the nature of the nuclear 

 membrane, there is much discussion whether it is part of the 

 nucleus proper or only an inner layer of the cell-protoplasm 

 enclosing the nuclear cavity. With the latter, and usually in- 

 visible in the resting nucleus in its living state, are numerous 

 slender threads the " nuclear filaments," which are closely crowd- 

 ed together and so intertwined that it is almost impossible, even 

 when carefully stained, to trace their limits with any certainty, 

 and until recently it was supposed thai they were fused together 

 at certain points, and formed a sort of net-work. This however 

 seems now not to be the case and the filaments are probably en- 

 tirely separate even in the resting nucleus. 



If we treat the nucleus with alcohol, chromic acid or any of 

 the various fixing agents, and then stain it, the structure may 

 be plainly seen. The filaments now show two parts, a colorless 

 matrix, and larger or smaller, deeply stained granules embedded 



