Dec. 29, 1887] 



NATURE 



205 



numerous that the unaided eye can scarcely distinguish 

 them, or the differences between the spring and autumn 

 wood are so indistinctly marked that they may appear 

 to be absent, or are at least obscure, as in the Olive, 

 Holly, and Orange, for instance. It is in the tropics, 

 however, that timber without annual rings is most 

 common, chiefly because the seasons of growth are not 

 sufficiently separated by periods of rest to cause the 



Pig. 7. — Transverse section of the wood of /'tiw^'i/w/a^/rti^r^, Vent., selected 

 to show a type of timber not uncommon in India. No distinct annual 

 rings appear, but the wood is traversed by wavy bands of tissue, which 

 may run into one another or not. The vessels (" pores ") are few and 

 scattered, and differ in size ; the medullary rays well marked, but not 

 large. To this type — differing in other details — belong many species of 

 figs, acacias, and other Asiatic Leguminosese, &c. 



formation of sharply-marked zones, corresponding to 

 spring and autumn wood, e.g. some Indian Leguminosaj, 

 &c. Zones of tissue of other kinds often occur in such 

 timbers, and have to be understood, since they affect the 

 properties of the wood very differently, e.g. some of the 

 Figs. 



None of the conifers or dicotyledonous trees, however, 

 are devoid of medullary rays, and distinctive characters 



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Fig. 8. — Transverse section of wood of Tamarind ns iiniica, Linn., selected 

 to show a not uncommon type of Asiatic limber. The annual rings are 

 indistinct, but occasionally indicated by denser tissue (a). The vessels 

 are fairly large and few, and scattered much as in Fig. 7, but there are 

 no such broad bands of cells as there. 



are based on the breadth and numbers of these : as 

 examples for contrast may be cited the fine rays of the 

 Pines and Firs, and the coarse obvious ones of the Oaks. 

 Again, the prominence or minuteness, or even (Coni- 

 ferae) absence, of vessels in the secondary wood afford 

 characters for classification. The contrast between the 

 extremely small vessels of the Box and the very large 

 ones of some Oaks and the Chestnut, for instance, is too 



striking to be overlooked. Then, again, in some timbers 

 the vessels are distributed more or less equably through- 

 out the " annual ring," as in the Alder, some Willows 

 and Poplars, &c. ; whereas in the Chestnut and others 

 they are especially grouped at the inner side of the annual 

 zone {i.e. in the spring wood), and in some cases these 



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Fig. g. — Tr.insverse fection of the wood of .leer pseiido-filatanus, selected 

 to show a type of timber common in Europe. The annual rings (a) are 

 well-marked and regular. The vessels are small and numerous, and 

 scattered somewhat equally over the whole breadth of the ring. The 

 medullary rays are numerous, some broad, some fine. Many European 

 timbers (beech, hornbeam, lime, &c.) agree with this type, except \ya 

 details. 



groupings are such as to form characteristic figures on 

 the transverse section, as in some Oaks, Rhamnus, &c. 

 In the woodcuts (Figs. 7-10) I have given four examples 

 illustrating a few of the chief points here adverted to. 



Passing over peculiar appearances due to the distribu- 

 tion of the wood-parenchyma between the vessels, as 



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Fig. 10. — ^Transverse section of wood of the common e\m(i/l>iins campes- 

 tri's), selected as a common type of European timber. The annual 

 rings are very distinct, owing to the large vessels in the spring wood ; 

 the vessels formed during the summer an 1 autumn are grouped in barids 

 or zones. The medullary rays are numerous, but not very broad. The 

 oak, ash, chestnut, and otheri agree in the main with this type, differing 

 chiefly in the mode of grouping of the smaller vessels, and in the 

 breadth of the medullary rays. 



exemplified by the Figs and the Maples, as well as minor 

 but conspicuous features which enable experts to recog- 

 nize the timber of certain trees almost at a glance, I may 

 now proceed to indicate a few other peculiarities which 

 distinguish different timbers. 

 The weight of equal volumes of different woods differs 



