28 Methods in Plant Histology 



35 per cent or 50 per cent alcohol. There is likely to be some 

 swelling, but spindles of mitotic figures stain well. It would be 

 worth while to try this solution with embryo-sacs of angiosperms 

 and with early stages in the female garnet ophyte of gymnosperms. 



CORROSIVE SUBLIMATE 



Corrosive sublimate, or bichloride of mercury, is soluble in water 

 and in alcohol. About 5 g. will make a saturated solution in 100 c.c. 

 of water. It is somewhat more soluble in alcohol, but for practical 

 purposes 5 g. in 100 c.c. of 50 per cent alcohol may be regarded as a 

 saturated solution. Corrosive sublimate used alone does not give 

 as good results as when mixed with acetic acid, chloroform, or picric 

 acid. Fixing is very rapid, the material being fixed almost as soon 

 as it is penetrated by the fluid. Material which is at all transparent, 

 like some ovules and the endosperm of gymnosperms before the 

 formation of starch, becomes opaque as soon as fixed, and so the time 

 needed for fixing is easily determined. From 10 minutes to one 

 hour should be sufficient for onion root-tips or lily ovaries. Smaller 

 or larger objects require shorter or longer periods. When used hot 

 (85 C.), the fixing is much more rapid. Filamentous algae or fungi 

 are simply dipped into the fixing agent and immediately taken out. 

 One minute is enough for onion root-tips, and two minutes is enough 

 for a lily ovary at the fertilization period. 



Wash out aqueous solutions with water and alcoholic solutions 

 with alcohol. In either case, the washing must be very thorough, 

 since preparations from incompletely washed material are sure to be 

 disfigured by crystals of corrosive sublimate. After material fixed 

 in the alcoholic solution has been washed in alcohol for several hours, 

 add to the 50 per cent alcohol a little of the iodine solution used 

 in testing for starch. It will impart a brownish color to the alcohol, 

 but the color will disappear in a few seconds, and the alcohol will 

 become clear if any corrosive sublimate remains. Add more and 

 more iodine until the brown color fails to disappear. The washing is 

 then complete. 



Material fixed in aqueous solutions should be passed through the 

 alcohols as described under "Dehydrating Agents," a few pages 

 farther on before using the iodine. 



