62 DESCRIPTIVE CATALOGUE 



GENERAL REMARKS ON TEE PRESENT IDENTIFICATION OP 

 CONIFEROUS WOODS. 



As will be gathered even from the short resume of the many 

 papers on coniferous woods given above, several of the older and 

 the more recent writers have laid stress on minutice which have 

 since proved to be merely individual variations and to have no 

 specific value. Thus in man} T of the older papers diagnoses 

 depended on the number of elements per annual ring, or on 

 the size of the tracheids, or the height of the medullary rays. 

 Careful study of living and fossil plants proves that these cha- 

 racters vary widely in the same individual, according to the age 

 and time of development of the part of the wood examined ; 

 and that in two individuals of the same species great differences 

 in these points are due to local differences of climate, soil, etc. 

 As a consequence, many of the diagnoses, and sometimes the 

 elaborate descriptions of wood-species, can no longer hold. 

 " Genera " even have been founded on what were merely 

 individual differences- for instance, fossils described separately 

 as Rhizocnpwssiii'ovylon arid CGrmwupressirto^ijloii by Con went 7, 

 can be paralleled from parts of the same stem within a single 

 year's growth, as has been pointed out by Krausel (1913). 



Even recent papers are often overloaded by elaborate measure- 

 ments of trncheid-si/e, wall-thickness, or the diameter of the 

 border of the bordered pits. For example, Barber (1898), in 

 his account of a Cupressmovijlon, gives hundreds of measure- 

 ments, and publishes tables illustrating minute variations 

 which are entirely devoid of profound significance. Average 

 measurements within certain rather wide limits are useful 

 secondary characters, but it may now be confidently stated that 

 the following details, which have so often in the past been made 

 the chief basis for specific determination, are actually worthless 

 as diagnostic characters : width of annual rings and number 

 of cells composing them ; thickness of tracheid-walis ; diameter 

 of border or of pit in bordered pits ; comparatively trivial 

 differences in the height of medullary rays (though here it may 

 be noted that if in ivoods of the same age wide differences occur, 

 such as one wood having generally about 80 and another generally 

 2 cells in its rays, such a feature is of some value) ; differences 



