28 ACOTYLEDONE^E. 



ral, vegetable, and animal substances, but actually 

 within them. However close the texture of rocks 

 and stones, vegetation attaches itself to them. The 

 discolorations or weather stains on these and on 

 buildings are caused by the presence of Lichens, 

 Conferva, &c. ; and wood of all kinds is the habitat 

 of numerous Fungi. These last not only exist on 

 the exterior, but penetrate and even decompose the 

 hardest timber. The dry-rot appears to be no other 

 than the seizure and destruction of a fungus* ; and from 



* Whether the dry-rot, Merulius destruens he the cause, or 

 only the effect of decay in timher is a point not yet sufficiently ascer- 

 tained hy naturalists. As many of the congeners of this plant affect 

 rotten vegetahle suhstances, it is quite natural to suppose that decay 

 precedes the attack of the fungus, and therefore the conclusion is, 

 that timber so destroyed, must have heen either imperfectly sea- 

 soned, or laid in a place deficient of due ventilation. It is well 

 known that the hasement timbers of buildings are more liable to 

 dry-rot, than those on the upper stories, and that if oil-cloth or 

 other covering impenetrable to air and moisture lie long unmoved in 

 the same place, dry-rot will appear sooner or later in the boards 

 beneath ; showing decidedly, that in such cases, want of free air invites 

 merulius. But to what can we impute the decomposition of the 

 massive ribs of a ship of war, while yet on the stocks, and before 

 being either planked or sheathed, and exposed to full and dry air for 

 two or three years ? Here there is neither oil cloth or paint to 

 shut in sap that might be detrimental ; on the contrary, every pre- 

 caution is taken that the scantling be perfectly seasoned. Still 

 before the ship is launched, these timbers, though apparently sound 

 and perfect to the eye, are found defective the interior being only 

 a mass of dust. If we examine its progress we shall see that the 

 sound wood is divided from the unsound by a very slender line ; 

 and that the fibrous tissue of the plant appears to absorb the juice 

 and decompose the cellular structure of the wood. 



