IS THE STEONGEST. 413 



undertakes to prove, upon physiological principles, that fast- 

 grown timber must necessarily be bad. He says that the effect 

 of an improved soil, climate, and situation, is to expand the 

 parts of the whole vegetable ; that cutting off part of the 

 vegetable above the ground will expand those parts that 

 remain; and he illustrates this his notion about timber by 

 reference to Lettuces, Cabbages, Spinage, and other esculents, 

 which he says are softer the faster they grow, and also to 

 Willows, Poplars, Easpberries, &c., which he says are the 

 fastest-growing of aU woody plants, and the softest-wooded. 

 Therefore, he continues, " whatever tends to increase the 

 growth of a tree tends likewise to expand the vegetable fibre ; 

 and whenever the vegetable fibre is expanded, the timber must 

 be less hard, and more permeable by air, &c., and of course 

 inferior for all purposes of timber." These speculations are 

 described by another writer as " interesting, ingenious, and 

 philosophical." I must therefore suppose them to have carried 

 conviction to some minds. In truth, howevef, they are a 

 tissue of absurdity, evincing a total ignorance of the nature of 

 vegetable organization. 



All plants consist of one or other of two substances — ^the one 

 cellular, the other fibro -vascular. The former is composed of 

 roundish cells, the latter of long tubes ; both are termed tissue 

 by physiologists. The cellular tissue, or substance, is brittle, 

 has little force of adhesion, and gives to the parts in which it 

 occurs the texture of a mushroom, or of the pith in an Elder 

 bush. On the other hand, fibro-vascular tissue is tough and 

 strong in various degrees, but in all cases much more tough 

 and strong than the cellular ; its nature, in a separate state, 

 may be compared to that of hemp, flax, or other vegetable 

 fibres, which are always composed of fibro-vascular substance. 



Timber consists of these two tissues intermixed ; when it 

 grows fast, it produces a large quantity of fibro-vascular tissue, 

 and but little ceUular ; when it grows slowly, it is more cellular 

 than fibro-vascular. There is never any expansion of the fibro- 

 vascular parts ; all that happens is that the aggregate number 

 of the latter is increased. Thus, suppose a stick an iuch in 

 diameter contains 500 tubes ; if you make it grow twice as fast, 



