134 METHODS IN PLANT HISTOLOGY 



extracted from the celloidin, or at least until the celloidin retains only a 

 faint pinkish color. Wash in 70 per cent alcohol (not acid) until the 

 characteristic purple color of the haematoxylin replaces the red due 

 to the acid. Stain in eosin (preferably a 1 per cent solution in 70 per 

 cent alcohol) for 2-5 minutes. Dehydrate in 95 per cent alcohol for 

 about 5 minutes. Absolute alcohol must not be used, unless it is de- 

 sirable to remove the celloidin matrix. Eycleshymer's clearing fluid 

 (equal parts of cedar oil, bergamot oil, and carbolic acid) clears readily 

 from 95 per cent alcohol. Mount in balsam. 



If serial sections are necessary, arrange the sections upon a slide, 

 using enough 70 per cent alcohol to keep the sections moist, but not 

 enough to allow them to float. Cover the sections with a strip of thin 

 toilet paper, which can be kept in place by winding with fine thread. 

 After the sections have been stained and cleared, remove the excess of 

 clearing fluid by pressing rather firmly with a piece of blotting-paper. 

 Then remove the toilet paper and mount in balsam. 



With occasional slight modifications, we have used the method as 

 presented by Eycleshymer in his classes. Instead of the graded series 

 of celloidin solutions, we use a 2 per cent solution, which is allowed to 

 concentrate slowly by removing the cork occasionally, or by using a 

 cork which does not fit very tightly. The material is imbedded when 

 the solution reaches the consistency of a very thick oil. If the material 

 is to be cut immediately, we prefer to imbed it and fasten it to the 

 block at the same time. The blocks should have surface enough to 

 accommodate the objects, and should be about I inch thick. White 

 pine makes good blocks; cork is much inferior. Tie a piece of ledger 

 linen paper around the top of the block, letting it project above the 

 top of the block far enough to make for the object a little tray with the 

 end of the block for a bottom. 



Place the block for a moment in ether-alcohol and then dip into the 

 2 per cent celloidin the end of the block which was left rough by the 

 saw. With the forceps remove a piece of the material from the thick 

 celloidin and place it upon the block, taking care to keep it right side 

 up. Dip the block with its object first in thick celloidin, then in thin, 

 and after exposing to the air for a few minutes drop it into chloro- 

 form, where it should remain for about 10-20 hours. It should then be 

 placed in equal parts of glycerin and 95 per cent alcohol, where it may 

 be kept indefinitely. If the material is hard, like many woody stems, 

 it will cut better after remaining in this mixture for a couple of weeks. 



