64 THE AMERICAN MONTHLY [Mch 



obliged to work over a few drugs, and for the reat have 

 to be content to acquaint themselves with the microscopic 

 characters as exhibited in drawings aud mounted speci- 

 mens. Drawings are always more or less diagrammatic. 

 They should not be relied upon by the student for the rec- 

 ognition of microscopical preparations of drugs. To the 

 expert a drawing may be of value, but the student should 

 look upon it simply as a key to assist in identifying the 

 tissues and cells in an actual specimen. Mounted sections 

 are, therefore, greatly to he preferred; but the tempta- 

 tion to indulge in so-called "spotting" should be strictly 

 avoided, because of the numerous pitfalls into which the 

 "spotter" may fall. Anyone trusting for the recognition 

 of a section to the tout ensemble maybe easily misled by 

 dfFerences between stained and unstained material, clear- 

 ed and uncleared specimens, glycerin, glycerin jelly, and 

 balsam mounting media, as well as by variations in the 

 size and age of the plant from which the sections have 

 been cut. For the most part the cursory examination 

 which many students vouchsafe to specimens of this class 

 is quite unproductive of knowledge, and in some cases 

 may lead to positive confusion. It is clear that only a 

 systematic examination of every specimen can be of any 

 real value, and it seems desirable to indicate some lines 

 upon which such an examination may be undertaken. 



The characters to wliich attention should be directed 

 fall into two categories, namely, those inherent in the 

 mounted specimen, and those resulting from the methods 

 of preparation. Dealing with the latter first, the varia- 

 tions due to mounting media, stains, and methods of 

 clearing should be noted. 



Mounting Media. -^Those most generally used are 

 Canada balsam aud glycerin jelly; more rarely used are 

 glycerin, dammar, carbolized water, and, still more rarely, 

 solutions of potassium acetate and calcium chloride. Sec- 

 tions of plant structures put up in glycerin jelly, glyce- 



