[I'ENiiALLowJ N. AMERICAN TAXACEyE AND CONIFERyE 37 



Avhich they are returned to the alcohol. One such treatment is sufficient 

 for most woods, but in some cases the process requires to be repeated sev- 

 eral times before the air is fully dislodged. Alter thorough dehydration 

 in alcohol, the sections require to be stained. My experience has been 

 that there are very few woods that can be successfully studied in balsam- 

 mounts without staining. These are the Sequoias^ most of the Taxaceœ, 

 and some of the junipers — in short, those woods which possess a natural 

 pigment in sufficient quantity to give them a pronounced colour. In all 

 other Coniferœ the effect of a highly refractive medium like balsam is to 

 render many details of structure wholly invisible or recognizable with 

 difficulty. The stain found best suited to the purpose is a strong' alco- 

 holic solution of Bismarck brown. It has the special advantage of dura- 

 bility ; it is applied easily and rapidly ; any excess is easily reduced by 

 the action of alcohol, and it is actinically opaque, thus making it of special 

 value in photographic work. Some woods absorb the stain very rapidly, 

 others but slowly, but an immersion of from three to five minutes is 

 ample for most cases. 



The sections are somewhat overstained. They are then thoroughly 

 washed in strong alcohol and cleared in carbolic acid, which serves to 

 reduce the stain to the proper degree of intensity. I prefer carbolic acid 

 to other clearing agents for hard tissues, since it clears more sharply and 

 quickly, but it demands the subsequent use of chloroform balsam for 

 mounting, instead of xylol balsam. In the latter case xylol would require 

 to be used as the clearing agent, but as small quantities of alcohol do not 

 dissolve in it with readiness, the subsequent mount is sure to come out 

 cloudy. The only other precaution to be observed is that, before trans- 

 ferring the section to balsam, all carbolic acid should be carefully drained 

 ofF. since any excess will be sure to remain in the preparation, and after 

 a time separate out in unsightly sphere-crj-stals. The mounts thus made 

 require to be dried slowly for about three or four days, to avoid the 

 formation of bubbles, but after that the drying may be carried on more 

 rapidly. 



In determining material, the sections should in all cases be carefully 

 prepared as directed. Any attempt to determine either genus or species 

 from poorly prepared material will be sure to lead to confusion. Finally, 

 with the sections properly mounted, a complete diagnosis should be made 

 and carefully written out. This is then employed in the determination. 

 Too much insistance cannot be laid upon the importance of observing 

 this rule, until one has gained a very large amount of expei'ienee, since it 

 is a very difficult matter to correctly carry in the mind and accurately 

 compare the large number of similar microscopic details required in the 

 determination of a species. 



Nomenclature is not a leading element in the present pajjer, and I 

 have considered that in adopting the "Index Kewensis " as a standard 



