1886.] on New Applications of the Mechanical Properties of Cork. 441 



C. A. Friend, the Resident Engineer of the Seville Waterworks, to 

 whom I am also indebted for this branch of a cork tree, these acorns, 

 this axe used in getting the cork, and for a description of the habits 

 of the tree, its cultivation, and the mode of gathering the harvest. 



The cork oak attains a height of thirty to forty feet ; it is not 

 cultivated in any way, but grows like trees in a park. The first crop 

 is not gathered till the tree is thirty years old, the next nine or ten 

 years later ; — both these crops yield inferior cork, but at the third 

 crop, gathered when the tree is fifty years old, the bark has attained 

 full maturity, and after that will yield the highest quality of cork 

 every nine or ten years. In the autumn of the year, when the bark 

 is in a fit state, that is, for small trees, from three-quarters of an inch 

 to one inch thick, and for larger ones up to one and a half inch, a 

 horizontal cut is made, by means of a light axe like the one I hold in 

 my hand, through the bark a few inches above the ground ; succeeding 

 cuts are made at distances of about a yard, up to the branches, and 

 even along some of the large ones, then two or more vertical cuts, 

 according to the size of the tree, and the bark is ripped off by inserting 

 the v>'-edge-shaped end of the axe-handle. In making the cuts great 

 care is taken to avoid wounding the inner bark, upon the integrity of 

 which the health of the tree depends ; but where this precaution is 

 taken, the gathering of the cork does not in any way injure the tree. 



After stripjDing, the cork is immersed for about an hour in hot 

 water, it is dressed with a kind of spokeshave, then laid out flat and 

 weighted in order to take out the curvature ; it is then stacked in the 

 open air, without protection of any kind, for cork does not appear to 

 be susceptible of receiving injury from the weather. 



The minute structure of the bark is very remarkable. First, I 

 project on the screen a microscopic section of the wood of the cork 

 tree. It is taken in a horizontal plane, and I ask you to notice the 

 diversity of the structure, and especially the presence of large tubes 

 or pipes. I next exhibit a section taken in the same plane of the corky 

 portion of the bark, Fig. 2. You see the whole substance is made up 

 of minute many-sided cells about -j-^o ^^^^ ^^ diameter and about 

 twice as long, the long way of the cells being disposed radially to 

 the trunk. The walls of the cells are extremely thin, and yet they 

 are wonderfully impervious to liquids. Looked at by reflected light, 

 if the specimen be turned, bands of silvery light alternate with bands 

 of comparative darkness, showing that the cells are built on end to 

 end in regular order. The vertical section next exhibited, Fig. 1, shows 

 a cross-section of the cells looking like a minute honey-comb. In some 

 specimens large numbers of crystals are found. These could not be 

 distinguished from the detached elementary spindle-shaped cells, of 

 which woody fibre is made up, were it not for the powerful means of 

 analysis we have in polarized light. I need hardly explain to an 

 audience in this Institution that light passed through a Nicol prism 

 becomes polarized, that is to say, tl^ vibrations of the luminiferous 

 ether are all reduced to vibrations in one i^lane, and, consequently, if 



