20 INTRODUCTION. 



alcoholic solution of anilin green. In a row of watch-crystals 

 the following liquids are placed: (1) water, (2) Woodward's 

 carmin, (3, 4, 5) alcohol, (6) absolute alcohol, (7) oil of cloves. 

 The specimen, taken from the green, is dipped for a moment in 

 water, then for about a minute in the carmin, then successively 

 through the alcohols, in each of which it remains ten to twenty 

 minutes, except in the first, where it remains only long enough 

 to have the unfixed carmin washed away. From the last alcohol 

 it goes into oil of cloves (or benzol), where it should remain 

 long enough to become perfectly transparent. It is then to l>e 

 mounted in balsam. 



96. Double-staining can also be effected by the successive use 

 of hsematoxylin and an anilin color. By the use of two or more 

 anilin dyes different parts of a specimen may be colored differ- 

 ently ; but as a rule all these effects are uncertain, and cannot be 

 relied upon for the positive identification of tissues. In general, 

 however, long bast fibres take characteristic colors. 



97. The following combinations for double-staining are rec- 

 ommended by Dr. Stirling, 1 and though originally designed only 

 for animal tissues, serve well with sections of plants : 



1. Osmic acid and picrocannin. 2. Picric acid and piero- 

 carmin. 3. Picrocarmin and logwood (htematoxylin). 4. Pi- 

 crocarmin and an anilin dye. />. Logwood and iodine green. 

 6. Eosin and iodine green. 7. Eosin and logwood. 8. Gold 

 chloride and an anilin dye. 



98. In the cases which require special treatment, for instance, 

 the staining of the nucleus, the precautions laid down must 

 be attended to in order to insure success. But in the ordinary 

 instances where it is desirable to stain a specimen merely to 

 bring some part into prominence for purposes of demonstration, 

 the widest choice in dyes and their use is advised. A few mor- 

 dants have been tried in order to fix the colors, but with little 

 success. The best are tannin in solution, and aqueous solutions 

 of any of the alums. A little practice will show which mordant 

 is best for each case. 



99. Specimens stained by nearly all of the above dyes can 

 be mounted securely in balsam, as directed in section 110; but 

 glycerin and glycerin-jelly mounts are apt to become faded or 

 discolored after a time. 



100. Mounting-media. Pollen and other dry specimens are 

 served in shallow cells formed by a thin ring of asphalt- 



1 Journ. Anat. aqd Phys., 1881, p. 34$, 



