THE ELEMENTS OF VEGETABLE HISTOLOGY 



killing the tissues is unnecessary. The specimen is 

 immediately immersed in the low-concentration alcohol 

 and carried through in the manner prescribed for 

 materials in which fixing is necessary. The details of 

 the dehydration of materials may be summarized as 

 follows: 



1 . Immerse specimen in alcohol 30 per cent for twenty-four hours 



2. 

 3. 

 4. 

 6. 

 6. 

 7. 



50 



70 " " " 



95 " 



absolute (a) for twenty-four hours? 



(6) " six " 



chloroform for three to six hours 



Clearing. The object of clearing is to make the cell 

 walls and contents more translucent. Due to the 

 action of the dehydrating medium, or on account of the 

 nature of the specimen, the cell walls may be more 

 or less opaque. The clearing agent corrects this con- 

 dition and enables us to see structures which, because 

 of this opacity, would not otherwise be apparent. In 

 dealing with vegetable materials possessing thin and 

 semi-transparent walls clearing may not be necessary. 

 But even with such materials it is advisable to immerse 

 the specimen, if only for a short time, in a clearing fluid 

 in order to assure a more thorough penetration of the 

 tissues by the paraffin. The use of chloroform after 

 the absolute alcohol partly serves this purpose. The 

 clearing agents employed include clove oil, cedar oil, 

 turpentine oil, phenol and xylol and mixtures of these. 

 After dehydration the specimens are placed in the 

 clearing fluid for a period of from six to twenty-four 

 hours, depending upon the texture and size of the speci- 

 men. The material should become almost transparent 



