PRACTICAL HINTS 



artificial, as the material is largely unworked ; but I trust and 

 believe that the future will provide material for an advance in 

 the right direction. Little attempt has been made to classify 

 woods according to their structure; yet there are characters 

 which seem to have a distinct systematic value. The primary 

 distinction between the wood of the Monocotyledonous trees 

 (Endogens) and that of the Broad-leaved Trees and the Conifers 

 is very definite and well known. The next, between the wood of 

 the two latter groups, is equally emphatic and in accordance with 

 the natural system. Up to this point the structure of the wood 

 has long been accepted as being of equal systematic value to 

 that of any other part of the plant. Taking the Conifers in their 

 turn, there are reliable differences between the woods of the Pines 

 and their allies and those of the Cedars, Cypresses, etc., and there 

 is a further sharp distinction between those Coniferous woods 

 with vertical resin canals and those in which they fail. But 

 when dealing with the wood of the Broad-leaved trees the 

 systematic botanists cannot be followed ; and though characters 

 run through long series of species, genera, and even orders, 

 there are so many exceptions that the task of reducing them to 

 an orderly arrangement seems almost impossible. 



It is not unnatural to assume that woods possessing two kinds 

 of rays should be grouped apart from those having but one kind ; 

 but by separating them we cut off the Cupulifera?, the Casuarinea? 

 and the Proteaces, and perhaps many other orders yet unworked, 

 from the remainder of the Broad-leaved trees, making an artificial 

 group of unrelated plants. Therefore our classification cannot 

 be based upon this feature. The arrangement of the pores is 

 very characteristic of many orders, and is very constant through- 

 out long series of species, as the Cupuliferae, the Myrtaceae, 

 the Proteacese and the Urticacese, but similar arrangements of 

 the pores can be found in quite unrelated orders. 



Again, the soft-tissue or wood parenchyma is equally casual 

 in its appearance, and, from the study of Solereder's work 

 I conclude that the minute structure of the wood, the pitting 

 of the cells, etc., is also unsuitable as a basis. 



Any one of the various kinds of tissue may be absent except 

 the wood fibres and the rays, and the following alternatives may 

 be found — 



i. Wood fibres and rays. 



2. Wood fibres, rays, and pores (vessels): 



3. Wood fibres, rays, pores, and soft-tissue (wood paren- 

 chyma). 



4. Wood fibres, rays of two kinds, and soft-tissue. 



5. Wood fibres, rays of two kinds and soft tissue of two 

 systems. 



xxxix 



