82 Methods in Plant Histology 



inches in length, taking the greatest care not to strain the tissues. 

 If the rhizome has been cut carelessly or pulled up, as is usually the 

 case, the finished mount will show ruptures between the bundles and 

 bundle sheaths, making your work look like the preparations sold 

 by optical companies. 



While the material is still fresh and moist, cut the sections and 

 place them at once in 95 per cent alcohol, where they should remain 

 20 to 30 minutes. It is not necessary to use a large quantity of 

 alcohol; 10 c.c. is enough for 100 thin sections of the rhizome. 



Pour off the alcohol and pour on an alcoholic solution of safranin 

 (a 1 per cent solution of safranin in 50 per cent alcohol. See chap. 

 xxix on " Formulae for Reagents")- It is better to let the safranin 

 act over night, or even for 24 hours. 



Pour off the safranin (which may be used repeatedly) and pour 

 on 50 per cent alcohol. The alcohol will gradually wash out the 

 safranin, but this stain is washed out more rapidly from cellulose 

 walls than from those which are lignified. The sections should 

 remain in the alcohol until the stain is nearly but not quite washed 

 out from the cellulose walls, while still showing a brilliant red in the 

 large lignified tracheids. If 5 or 10 minutes in the alcohol draws the 

 safranin from the lignified walls as well as the cellulose, stain longer; 

 if the differentiation is not secured in 5 or 10 minutes, a small drop of 

 hydrochloric acid added to the alcohol will hasten the process. 

 Some recommend staining for only 1 or 2 hours, but the washing-out 

 process is likely to be rapid and uncertain. 



Pour off the alcohol and wash the sections thoroughly in ordinary 

 drinking-water. The washing should be particularly thorough if 

 acid has been used to hasten the previous process, for the preparations 

 will fade if any acid remains. 



Stain in Delafield's haematoxylin 3 to 30 minutes. Usually 5 

 minutes will be about right. Delafield's haematoxylin will stain 

 the cellulose walls, but will have little or no effect upon lignified 

 structures. 



Transfer to drinking-water, not distilled water. The red color 

 of the whole section, as it appears to the naked eye, will be rapidly 

 replaced by a rich purple. Continue to wash in water for 2 or 3 



