PRACTICAL HINTS 



no training in botany and who, I am certain, will part company 

 with me if I expect them to expend valuable time in the laborious 

 process of micrometric measurement. Moreover, to see the fine 

 lines of the micrometer upon the image of wood sections mounted 

 dry is a task in which I have not yet succeeded, and therefore the 

 mounting in some medium becomes necessary. Even then the 

 strain of seeing the micrometer lines upon the image of dark 

 coloured woods is more than the eyesight can bear for any length 

 of time. Measurement by groups, on the other hand, is a ready 

 and simple method, but presupposes the possession of a series 

 of similar sections of woods corresponding to the type of the 

 group. For instance, I employ the Common Oak for ' Size or 

 Group II.', and lay a thin section of that wood side by side with the 

 specimen to be tested. If the largest pores of each are somewhat 

 of the same size the latter is said to fall under Size II. If not, 

 the other type sections representing other grades must be tried 

 in succession until the correct one be found. This seems a rough 

 method, but that it is the only practical one (and a very useful 

 one) will soon be seen when the great variation of the elements 

 in the annual rings of various ages, already discussed, is taken 

 into account. The type species which I have adopted are taken 

 from Nordlinger's list, and are, as far as possible, common or 

 readily obtainable woods, a principle I have adhered to in the 

 preparation of the scales of measurement of the rays and also 

 of the grade of hardness of woods. Gamble employs scales of 

 the same nature. I have been prompted to use Nordlinger's scales 

 by the desire for uniformity, so that any student may use my 

 figures in conjunction with the greater work without the labour of 

 translating every measurement. 



The counting of the rays and pores is most conveniently done 

 by means of a perforated piece of tin-foil having a hole exactly 

 i sq. mm. in area. When this is superimposed upon the section 

 to be tested, and one side of the square brought parallel to the 

 rays, the latter may be readily counted, and further, as the pores 

 are usually separated into narrow areas by the rays, the latter 

 assist in guiding the eye, thus saving the annoyance of losing 

 count. My practice, upon which the figures given in the de- 

 scriptive portion of the book are based, is to search for the part 

 where fewest rays or pores occur, and afterwards for that part 

 where they are most numerous. These give the minimum and 

 maximum figures for the specimen, which may be modified by 

 subsequent observation upon other specimens when they are 

 available. Another figure necessary for our purpose is the 

 number of pores in the individual groups, i.e. in actual contact 

 with each other. These groups are of the two kinds already 

 mentioned, the subdivided or mother-and-daughter groups, and 



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