116 FORESTRY INVESTIGATIONS U. S. DEPARTMENT OF AGRICULTURE. 



to utilize for purposes of identification tlic difference in the number, size, and distribution of these 

 rays, or the proportion between the number of rows of tracheids and those of parenchyma cells, 

 as was done by Dr. J. Schroeder, 1 lias not been successful, and appears of little promise. 



The large rays with transverse resin ducts resemble the smaller rays described. On PI. XXIV 

 at A such a ray is seen both in radial and tangential section. Series of transverse tracheids 

 occupy the upper and lower edge, but the interior, unlike that of common rays, is several 

 cells wide, and contains an open duct in its widest portion. (See PI. XXIV, r. <l.) This duct is 

 commonly more or less filled with resin (see PI. XXIV, K); it is surrounded by thin-walled secreting 

 cells, and, in the heart wood, often divided or tilled up by thylosis, i. e., by very thin walled, 

 much puffed out cells, growing out of the surrounding secreting cells before the latter perish. 



The walls of the secreting cells are quite thin, those of the. remainder of the parenchyma 

 vary to some extent in the different species. In the longleaf and loblolly pines the walls of the 

 parenchyma composing the principal part of the ray are generally quite thick (see PI. XXIV, A-E), 

 thicker than those of the cells of ordinary rays, and especially thickened near the simple pits by 

 which these cells communicate with each other. In Cuban and shortleaf this thickening is much 

 less conspicuous, and absent entirely in many cases (see PI. XXIV, A), while in the spruce pine it 

 seems wanting altogether. 



These ducts exist even in the very first ring (next to the pith), are smaller and more numerous 

 near center, but have essentially the same structure in the wood of the fifth and later years. 



The tracheids of the pith rays are wanting next to the pith, but occur in all rays in the outer 

 part of even the first ring. The rays in this ring are generally lower, composed of fewer cell rows, 

 but the cells are larger than the rest of the wood. 



Both shape and size of these medullary rays are very variable; an average of about 0.4 mm. 

 for the height of the ray and GO /i for the width at the resin duct was observed. An attempt 1o 

 utilize the shape, especially the appearance of the two edges, as a means of separating the wood 

 of these species has so far failed entirely. 



The large resin ducts running lengthwise in the wood or parallel to the common wood fibers 

 are much larger than the transverse ducts, measuring, inclusive of the secretive cells, on an 

 average about 0.2 mm. (0.008 inch) on their smaller radial diameter and about 0.3 mm. on tlie 

 tangential. (See PI. XX, A, r. d.) They are usually situated in the summerwood of each ring, 

 often in narrow rings, causing an irregular outline. They are smaller and more numerous near 

 the pith, here usually forming several series in one annual ring, more numerous in wide rings 

 than in narrow ones, but their number per square inch of cross section as well as their dimensions 

 appear to be Independent of the width of the rings. In their structure they resemble those of 

 other pines. They are surrounded by thin-walled resin -secreting parenchyma, part of which often 

 appears as if not directly connected with the duct. (See PI. XX, A.) In many cases all the 

 tissue between two neighboring ducts is of this parenchyma. Longitudinal and transverse ducts 

 frequently meet and thus form a continuous network of ducts throughout the wood. 



ECONOMIC; ASPECTS OF FOUEST KESOUBOES. 



One thousand million dollars is the value of the raw products which are annually derived 

 from the forests of the United States. 



There is no other resource, there is no other business or trade which approaches in magnitude 

 or importance, in production of values or in the intimate relation to all pursuits of life that which 

 is based upon the exploitation of our forest resources, excepting alone agriculture and its adjuncts. 



Professor James, in Bulletin 2 of the Division of Forestry, figured upon the basis of the 

 census for 1880 as follows: 



If to the value of the total output of all our veins of gold, silver, copper, lead, zinc, iron, and coal, were added 

 the value, derived from the petroleum wells and stone quarries, and this stun were increased by the estimated value 

 of all the steamboats, sailing vessels, canal boats, llatbciats, and barges, plying in American waters and belonging 

 to citizens of the United States, it would still be loss than the value of the forest crop by a sum sufficient to 

 purchase at cost of construction all the canals, buy at par all the stock of the telegraph companies, pay their 

 bonded debts, and construct and equip all telephone lines in the. United States. 



'Dr. Julius Schroeder, das llolz der Coniferen, Dresden, 1872. 



