l886.] NEW-YORK MICROSCOPICAL SOCIETY. 107 



THE STRUCTURE OF QUERCUS ALBA. 



BY P. H. DUDLEY, C. E. 

 {Read June \'ith, 1886.) 



This wood possesses a structure not only of scientific interest, 

 but one which renders it of economic value. The largte ducts 

 forming in the early spring growth are arranged in the inner 

 portion of the ring, in one, two, and sometimes three quite dis- 

 tinct concentric rows. Surrounding these ducts are small tra- 

 cheides, which form at the same time and have numerous small 

 thin places on their sides ; their cross section is like that of the 

 ducts, elliptical. 



In the normal growth of an annual ring, hard dense fibres, in 

 masses, begin to thicken the layer, soon after the ducts are 

 formed, and generally continue through to the outer portion. 



In wood of dense growth these fibres form the largest portion 

 of the layer, and the wood has a high specific gravity, reaching 

 in some specimens from .82 to .85 ; a cubic foot weighing 51 to 

 53 lbs., the ordinary weight being 42 to 45 lbs. These hard 

 fibres are very small, being only .0006 to .0075 of an inch in 

 diameter, and with the magnification of 100 diameters the lumen 

 is just visible. I have not been able to find thin places in these 

 fibres, though fluid communications may exist. These hard 

 fibres do not occur as a complete zone, as the hard fibres do in 

 several of the conifers, but are divided into radial layers or 

 masses, if the ring be thick, by smaller ducts which diminish in 

 size as they approach the exterior of the ring. These ducts are 

 also surrounded by the small tracheides. The medullary rays 

 are distributed through all classes of the fibres, the cells becom- 

 ing flattened as they curve around the ducts. These masses of 

 hard fibres are further subdivided by rows of cells running at 

 right angles to the medullary rays, and which, in the alburnum, 

 contain starch, except during the season of most active growth. 

 Such abundant provision (or the nourishment of the hard fibres 

 indicates that only a limited circulation takes place in them, 

 probably little more than is required for their development. 

 Some have considered these fibres purely mechanical, and only 

 added for strength. This prompts the inquiry, What additional 

 strength and hardness does the oak require in growing, more 



