108 • Journal of the [J^^IY) 



than many other species of trees which grow of equal size and 

 height and do not have similar fibres ? The Liriodendron Tulip- 

 ifera, a tree of even more stately dimensions and broader leaf, 

 has a series of ducts interspersed entirely through the annual 

 layer, but has no hard fibres, and has only about one-half the 

 specific gravity of the oak. 



The climatic conditions have much to do with the growth of 

 the hard fibres in the oak, for in some seasons the same tree will 

 only have a few in the annual rings. This lack of hard fibres 

 is noticeable in the timber which now comes to market ; timber 

 which contained more and which was, therefore, of a superior 

 quality, having been, apparently, exhausted. White oak, which 

 has but a few of the hard fibres in the rings, is brash, and not 

 as strong as that first described. In the transverse section, of 

 which I exhibit a photo-micrograph, only the small medullary 

 rays are seen, running through the masses of hard fibres. In 

 other sections, the primary rays can be seen passing through the 

 hard fibres. The starch-carrying cells, which also divide the 

 hard fibres, at right angles to the medullary rays, are clearly 

 indicated in the photo-micrograph. In the radial longitudinal 

 section, the medullary rays and the exterior and interior of one 

 of the ducts can be seen ; the latter are filled with tissue, and 

 are never empty ; the section also shows hard, dense fibres, also, 

 the interspersed starch-carrying cells. 



In the tangential section, can be seen the end of one of the 

 large primary bundles of medullary rays, also, those of the single 

 rows, the characteristic markings of the tracheides, and smaller 

 ducts. The short cells are those which at one time contained 

 starch. 



