THE GENUS DENDROCTONUS. 41 



Pitch tubes (figs. 8, 9, 100). — The resin or gum expelled by the 

 beetles from the entrance burrows is often formed into more or less 

 regular masses with a hole through the middle, thus suggesting the 

 name "pitch tubes." 



Infested trees. — Trees containing living parent adults or develop- 

 ing broods are referred to as " infested trees." 



Fading tops. — The fading or noticeably paler green of the foliage 

 of infested trees is referred to as " fading tops." 



Sorrel tops. — The yellowish foliage of trees dying from the attack 

 of the beetles is termed " sorrel tops. " It must be remembered that 

 a certain number of the older leaves or needles on the healthy twigs 

 die, turn yellow, and fall each year; therefore this normal condition 

 should not be mistaken for an indication of unhealthy conditions. 

 It is only when the needles of the middle and tip of the cluster turn 

 yellow from the base outward that the dying of the tree is indicated. 



Red tops. — The term "red tops" refers to the color of the foliage 

 after the tree is dead, and usually after the broods of destructive bee- 

 tles have emerged from the bark. This reddish-brown of the adher- 

 ing pine needles may prevail for one year or more after the trees are 

 dead. 



Beetle-abandoned trees. — After the broods of the destructive beetles 

 have emerged from the bark of a tree such a tree is referred to as 

 "beetle abandoned." 



Black tops (fig. 25). — The condition of the dead trees after all of 

 the needles have fallen and two or more years after the beetles have 

 left them is referred to under the name "black tops." 



Broken tops (figs. 26, 27). — After the trees have been dead four or 

 more years and the tops have broken off they are termed "broken 

 tops." 



Sap stain or blue sap (fig. 29). — The discolored condition of the sap- 

 wood of infested trees before and after the leaves begin to fade is 

 referred to as "sap stain" or "blue sap." 



Sap decay. — After the trees have been dead long enough for the 

 sapwood to be decayed, but the heartwood is yet in a sound condi- 

 tion they are termed "sap decayed." 



Heart decayed. — The term "heart decayed" refers to the condi- 

 tion after the trees have become unfit for any practical use. 



Millimeters and inches. — One millimeter equals about one twenty- 

 fifth of an inch or about four-hundredths of an inch. Two milli- 

 meters equal about one line, or about one-twelfth of an inch. To 

 reduce millimeters to inches, multiply by 0.04; to reduce hun- 

 dredths of an inch to millimeters divide by 0.04. To reduce lines to 

 millimeters multiply by 2; to reduce millimeters to lines, divide by 2. 



a Needles injured by climatic conditions have the tip dead and the base green. 



