36 ROYAL SOCIETY OF CANADA 



era. It is also true that from a radial section we may with certainty 

 distinguish Taxodium distichum from Sequoia and all other genera, and 

 that we may also sepai-ate the two species of this latter genus from one 

 another. But comparatively few woods are thus strongly characterized, 

 while in the genus Finns. Cwpres&us, Thuya., etc., the distinction between 

 one species and another often involves a consideration of several charac- 

 ters. Where species are thus separated by narrow lines, much judgment 

 is needed for their ditîerentiation, and a single section in an}' given dii'ec- 

 tion would be whoU}' inadequate to meet the requirements of the case. 

 Furthermore, the complete aspects of structure are exhibited only when 

 sections in three directions have been made and examined — one transverse 

 and two longitudinal — of which latter one must be radial and the other 

 tangential. Such sections should not exceed the one five-hundredth of an 

 inch in thickness, when, under proper treatment, they become perfectly 

 transparent and exhibit all the various details of structure in a very 

 satisfactory manner. 



With respect to the cutting, great care should be taken that the 

 plane of section is exactly transverse, radial or tangential as the case 

 may be, otherwise distortions of structure are introduced and the proper 

 details ai-e lost. In the case of tangential sections, it is of tirst import- 

 ance that they should represent as large an area as possible. In stems 

 of small diameter, such as alone may be obtained in the case of Juniperus 

 sabina procumbens^ or in the case of small branches, such as often repre- 

 sent the only available material of a fossil wood, where the total diameter 

 is less than one inch and the curvature of the growth-rings is correspond- 

 ingly short, it is often a diltieult matter to secure sutHcient area for a cor- 

 rect diagnosis. In all such cases a number of sections should be prepared 

 for examination, since the determination of such species as Abies nobilis, 

 Abies bracteata and Larix occidentalis depends in large measure upon 

 the structure thus displayed. For section cutting I have employed a 

 King microtome, with a knife of heavy weight and special form, and 

 found it to be fairl}^ satisfactory, particularly when the material is fresh 

 or joroperly softened. The sections are cut to the full size of the micro- 

 tome-well, and average about one centimetre square. 



The sections having been properly cut, require to be exhausted of all 

 air which they may contain. This is sometimes, especially in the spruces, 

 a troublesome process, but it may be managed by means of the air-pump, 

 or by the prolonged action of alcohol, when time is not an impoi tant ele- 

 ment. The method employed in the present case has been based upon 

 the dehydrating action of alcohol, in conjunction with the action of boil- 

 ing water, since all the structures involved are of such a nature as to be 

 subject to no alteration under such conditions. The usual procedure has 

 been to place the sections in alcohol for ten or fifteen minutes ; they are 

 then transferred directly to boiling water for about five minutes, after 



