WOOD OF SOUTHERN PINES. 



113 



middle. They are arranged in regular radial rows (see PI. XX), which are continuous through au 

 indefinite number of rings, but the number of rows increasing every year to accommodate the 

 increasing circumference of the growing stem. (See PI. XX, On) The libers of the same row 

 are practically conterminous, i. e., they all have about the same length, though at their ends they 

 are often bent, slightly distorted, and usually separated (see PI. XX, B c; also fig. 21), their 

 neighbors lilling out the interspaces. There is no constant difference in the dimensions of these 

 libers in the different species here considered. In every tree the libers are shortest and smallest 



A 



FIG. 22. Cross section of normal and stunted growth in Longleaf Pine. 



near the pith of any section, rapidly increasing in size from the pith outward, and reaching their 

 lull size in about the tenth to twentieth ring from the pith. To illustrate: In a section of longleaf 

 pine, 10 feet from the ground, the diameter of the tracheids in radial direction is in ^=0.001 mm.: 



H. Doc. 181 8 



