MISCELLANEOUS PAPERS. 409 



inch. One of the finest-grained woods of all is sweet-fruited juniper, 

 whose cells measure twelve to sixteen microns across, either radially 

 or tangentially ; and there are from 2,500,000 to 3,000,000 cells to the 

 square inch. These can scarcely be seen with the naked eye and can- 

 not be counted without the aid of a good compound microscope. 



The tallest trees are those having medium-sized cells, capillarity 

 being less in the larger cells, and trees with finer cells, such as the 

 cedars and junipers, having less capacity and requiring a highly spe- 

 cialized food, which is taken only in small quantity. Besides, the 

 sap is very heavy to start with in such trees, requiring and receiving 

 very little evaporation in elaboration. This accounts, too, for the 

 smallness of the leaves and the exceedingly slow growth of such trees. 



In almost all spring and summer wood of coniferous trees the cells 

 are extended or broadened radially ; in autumn and winter wood, on 

 the other hand, the cells are compressed radially, being less than half 

 the breadth of the early cells. The breadth of the cells tangentially 

 to the tree is limited by the distance apart of the radial plates. This 

 is very uniform, though slowly increasing from year to year until a 

 limit is reached ; then a cell divides radially and a new radial row of 

 cells and a new set of radial plates appear. Usually there are from 

 two to five or six radial rows of cells at any horizon between two radial 

 plates ; in the latter case the formation of a new radial plate reduces 

 the number of rows between plates to two or three. One-fourth of an 

 inch higher up or lower down in the tree the radial plates are in new 

 positions relatively to the vertical cells. 



The following table gives (1) the number of cells, ( a ) tangentially 

 and {b) radially, across the field of the microscope in cross-sections 

 of the various species of woods named. From these data are calculated 

 (2) the measurements, {a) tangentially and {h) radially, of the cells, 

 in microns or thousandths of a millimeter; (3) the number of cells in 

 a square millimeter; (4) the number of cells in a square inch, and 

 (5) thegradeof fineness of the grain of the wood," (1)" being coarse or 

 megacellular, " (2) " medium or mesocellular, and *' (8) " fine or micro- 

 cellular. Numerous examples were taken of each kind of wood and a 

 general average taken. Measurements of cells are of the cells com- 

 plete, including walls ; measurements of ducts are of the passages only. 



Instrument used : Bausch & Lomb compound, with substage con- 

 denser and no micrometer; eyepiece, one inch; objective, three- 

 fourths of an inch ; draw-tube closed; diameter of field, 1,587 to 1,610 

 microns, almost exactly one-sixteenth of an inch. Woods used: 

 Hough's sections of American woods. 



