22 ANATOMY OF THE GYMNOSPERMS 



carefully sharpened plane, which is, in some respects, one of the 

 very best of section cutters where the work does not call for the 

 most critical methods. Preferably the blocks which have been 

 boiled as described may be sectioned on a microtome in the 

 usual way. For this purpose any instrument which provides a 

 high degree of rigidity may be employed. 1 For purposes of very 

 exact study more elaborate methods and more expensive instru- 

 ments will have to be employed, but since these relate chiefly to 

 botanical laboratories where they are already well known, they 

 need not be specified here. 



For the purpose of freeing the sections from air, a somewhat 

 troublesome process where sections are prepared as specified, 

 the air pump may be used ; but a far more simple and less costly 

 method is to boil the sections in water for five or ten minutes and 

 then plunge them directly into 95 per cent alcohol. At intervals 

 of five minutes or so alternate the treatment with alcohol and 

 water, and, except in some of the most troublesome woods, such 

 as the spruces and larches, it will be found that the air is all dis- 

 charged in the course of half an hour. As a matter of precau- 

 tion the sections should then be left over night in 95 per cent 

 alcohol in order to secure complete dehydration. 



Before mounting in balsam the sections must be stained. For 

 this purpose almost any of the well-known aniline stains or 

 Delafield's hematoxylin may be employed, the object being to 

 secure a perfectly sharp and well-defined image on a clear field. 

 But in the study of woods it is often of importance to be able to 

 photograph what is seen, and as all the stains are not equally 

 valuable for this purpose the dye should be selected with special 

 reference to the results sought. Where instantaneous exposures 

 are to be employed nothing is better than Delafield's hema- 

 toxylin, which is allowed to act until a deep purple color is pro- 

 duced. But this stain will not answer for time exposures as well 



1 One of the best of simple instruments is the table microtome made by Bausch 

 and Lomb, but the knife used with this form of instrument should be a plane blade 

 mounted in a heavy wooden handle of such form as to secure a perfectly firm grip. 



