SPECIAL METHODS 151 



Bensley recommends the following method which we have found 

 rather uncertain, but which, when successful, yields magnificent prepa- 

 rations: On the slide, bleach for 2 or 3 seconds in a 1 per cent aqueous 

 solution of permanganate of potash ; then treat with a 5 per cent aque- 

 ous solution of oxalic acid until the preparation becomes white (a few 

 seconds); wash in water, and then stain as follows: 



1. Copper acetate (neutral) saturated solution in water, 5-10 minutes. 



2. Wash in water. 



3. One-half per cent haematoxylin, 5-10 minutes. 



4. Wash in water. 



5. Potassium dichromate (neutral), 5 per cent solution in water until the 

 preparation blackens, usually 30 seconds or less. 



6. Differentiate in Weigert's ferricyanide solution. 



Borax 2 . g. 



Ferricyanide of potassium 2 . 5 g. 



Water 200.0 c.c. 



7. Wash in water and proceed as usual. 



Yamanouchi's method. — Fix in a 10 per cent solution of neutral 

 formalin in water for 24 hours; wash in water, 24 hours; dehydrate, 

 leave objects as small as onion root-tips at least 24 hours in the 85 per 

 cent alcohol; clear in xylols; imbed; stain in iron-alum haematoxylin. 



CANALICULI 



By using special methods, Bensley has obtained views of the proto- 

 plasm of plants, quite different from those seen in ordinary prepara- 

 tions. In the cell of a root-tip a series of small canals, or vacuoles, 

 appears, which is much more definite and extensive than the usual dis- 

 play of vacuoles and which appears before any vacuoles can be recog- 

 nized in preparations made in the usual way (Fig. 27C). Being a 

 zoologist, he called these vacuoles canaliculi. 



GOURLEY'S METHOD FOR VASCULAR SYSTEM 



It is well known that if stems be cut under water in which there is 

 a dilute solution of aqueous eosin, the stain will rise in the bundles, 

 making them very prominent, but the material cannot be fixed and 

 cleared because the stain diffuses. In the fourth edition of this book it 

 was stated that such preparations would be still more valuable if they 

 could be fixed and cleared. Dr. Gourley has developed such a method 

 which is valuable, not only for stems, but for various other things. He 



