while in the sunjmer-wood the cavities are so narrow as to be 

 scarcely visible except under high magnification. Among the 

 fibrils and also running lengthwise are sometimes to be seen 

 slender tubes, larger than the fibrils, always very long, and filled 

 with resinous material. These resin ducts, as they are called, are 

 reservoirs of the pitch which oozes from trees like pines when 

 wounded. Such ducts appear on longitudinal surfaces as more or 

 less conspicuous, yellowish or brownish streaks. 



In many woods there are no resin ducts, but there are often 

 numerous, commonly empty, canals Sometimes considerably larger 

 than resin ducts and sometimes miuch smaller in diameter. They 

 form a continuovis system of tubes throughout the wood. They are 

 known as pores or vessels, and in the sap-wood serve as pipes or 

 reservoirs for conveying upward the crude sap absorbed by the 

 roots or for storing it together with more or less air temporarily 

 till needed. They thus share with the wood fibrils the office of 

 conduction which is performed alone by the fibrils of such woods 

 as pine. 



I. WITH PORES WHICH ARE DISTINCTLY OF UNEQUAL 

 SIZE (UNEQUAL-PORED) . * 



A. Summer pores in radial brcunchimg lines (radial-pored) . 



Oak (QuERCDs). Pith rays partly broad and conspicuous. 

 Chestnut (Castanea). Pith rays all minute. 



B. Summer pores in concentric, wavy and sometimes branching lines 



appearing as finely feathered hatchings on tangential sections 

 (arc-pored) . 



£!lin (Ulmus). Pith rays indistinct, heart-wood reddish brown ; sap- 

 wood greyish to reddish white. 



C. Summer pores scattered singly or in groups, imbedded in short lines 



of denser material which often connect the pores together into elon- 

 gated series more or less concentrically arranged (link-pored) . 



Common IiOCUSt (Robinia Psecdacaoia) . Summer pores in 

 clusters united to form conspicuous, wavy, broken lines, often branching ; 

 pith rays fine but distinct ; heart-wood reddish orange, sometimes tinged 

 with purple or green ; sap-wood yellow, particularly on transverse section ; 

 wood very heavy and hard. 



* A few new terms descriptive of structural ciiaracteristics that require more or less 

 elaborate definition are here suggested as labor-saTing conveniences for the student in 

 recording his obsei'vations. 



