456 XXXII. CELL-DIVISION AND NUCLEAK DIVISION. 



a number of slides can be stained together by placing one glass 

 crystallising dish within another of suitable size, weighting down 

 the inner one, e.g., with shot or sand, and filling the space between 

 the two with the staining fluid. It is safest to place the slides 

 section-face outwards. If the crystallising dishes have lips, these 

 can serve as starting-points in the placing and recognition of the 

 several object-slides. Several such crystallising dishes can be 

 placed within one another, the central one only being weighted. 

 This method also economises the staining material.] 



In purchasing stains it is of great importance to get those 

 which work correctly, and hence to obtain them from a firm who 

 are acquainted with the scientific needs of microtechnics. 1 The 

 best micro stains are those prepared by Dr. G. Griibler & Co. of 

 Leipzig. 



All the processes of nuclear division which show an interna 

 thread-like differentiation are collected together under the term 

 indirect or mitotic division, as opposed to the direct division, 

 which consists in a simple constriction of the nucleus. Such 

 direct nuclear division is often found in the older cells of higher 

 plants, and as an exceptional case in the actively growing inter- 

 nodal cells of the Characege (Stoneworts). 



Direct Nuclear Division. For the observation of direct or 

 amitotic nuclear division in older cells the older internodes of 

 Tradescantia Virginica are especially suited. A longitudinal 

 section, examined in water, shows them usually in considerable 

 number (Fig. 160, A). The nuclei show the same internal struc- 

 ture as before, but are, however, more or less irregularly constricted 

 into sections of various size and form. If the constriction is uni- 

 lateral, the nucleus appears kidney-shaped ; with constriction all 

 around, it shows as a figure of 8, or perhaps irregularly lobed. In 

 many cases the segments have completely separated, and lie either 

 in contact or more or less remote. The number of the nuclear 

 segments thus found in one cell can amount to eight or ten. They 

 are of various sizes. The nuclei in course of constriction are to be 

 found in almost all the elements in the section, most easily in the 

 parenchyma of the central cylinder. The nuclei can be fixed very 

 quickly with acetic methyl-green (Fig. 160, B), and are then very 

 sharply defined. 



1 Messrs. Southall Bros. & Barclay, Manufacturing Chemists and Scientific 

 Instrument Makers of Birmingham, have undertaken to keep Griibler's stains. 



