116 Methods in Plant Histology 



TRANSFER TO THE STAIN 



After the paraffin has been removed with xylol or turpentine, and 

 the xylol or turpentine has been rinsed off with alcohol, the next 

 step is the staining. If the stain is a strong alcoholic one (85 to 100 

 per cent alcohol), transfer directly to the stain. If the stain is in 

 70 per cent alcohol, pass through 95 and 85 per cent alcohol, 5 minutes 

 in each, before staining. If an aqueous stain is to be used, pass down 

 the whole series 95, 85, 70, 50, 35, and water 5 minutes in each, 

 before placing the slide in the stain. 



This is rather tedious, but, for cytological work, it seems to be 

 necessary. For general morphological work, the slide may be trans- 

 ferred directly from the absolute or 95 per cent alcohol to any stain. 



DEHYDRATING 



After the sections have been stained, they must be dehydrated. 

 If they have been stained in a strong alcoholic solution, transfer to 

 95 and then to 100 per cent alcohol, 5 minutes in each, if the stain does 

 not wash out too rapidly. If stained in an aqueous solution, pass 

 through the series, water, 35, 50 ,70, 85, 95, and 100 per cent alcohol, 

 about 5 minutes in each. 



With stains which wash out rapidly, the times must be shortened 

 and some of the alcohols must be omitted. With aqueous gentian- 

 violet, all must be omitted except the 95 and 100 per cent, and even 

 in these the time must be shortened to a few seconds. 



CLEARING 



After the sections have been dehydrated, they must be cleared, 

 or made transparent by some clearing agent. The clearing agent 

 must be a solvent of balsam, but it is not at all necessary that the 

 balsam shall be dissolved in the particular clearing agent which has 

 been used. Xylol balsam is used not only when preparations have 

 been cleared in xylol, but also when they have been cleared in clove 

 oil, cedar oil, bergamot oil, or other clearing agents. 



Xylol is the most generally useful clearing agent. Place the slide 

 in equal parts of xylol and absolute alcohol and then in pure xylol, 

 allowing each to act for about 5 minutes. 



