MISCELLANEOUS PAPERS. 415 



either in straight vertical rows or promiscuously, the lenticels being 

 from one cell thick at the lower and upper edges to 6, 10, 15 or more 

 cells in the thickest part, and from 50 to 500 or more cells in height. 

 Rays are sometimes one-fourth of an inch or more in breadth ( height ), 

 and often contain several thousand cells in a radial bundle or plate. 

 Such plates are very large and strong and hard, as in oak, sycamore, 

 chestnut, water locust. As in evergreen trees, the primary rays origi- 

 nate in the pith. All rays end in the bark. 



The comparative size of the ducts in a tree in any year seem to be 

 inversely proportional to the leafage for that year. The number or 

 size of the macropores does not vary much from year to year; but 

 greater leafage in any year causes a greater thickness of summer and 

 autumn wood with its accompanying micropores to be formed. Less 

 leafage causes less solid wood to be built up ; so that the relative 

 amount of spring wood is greater. In trees that live near or by the 

 edge of water, where the food supply is unvarying at all seasons, 

 the ducts are of uniform size and the wood of uniform texture 

 throughout the year. The same is true of trees that grow on moun- 

 tain sides, where the supply is constant and uniform, though never 

 superabundant. 



