26 CIRCULAR 3 3 3, U.S. DEPARTMENT OF AGRICULTURE 



into the crevices of the bark the figures remain legible for a much 

 longer period. 



Rubber stamps are in much greater favor in Europe than in 

 North America, owing largely to the fact that most sample-plot 

 work there involves only relatively small trees. Rubber-stamped 

 numbers are legible in much smaller sizes than numbers that are 

 applied freehand. As American investigations turn more to im- 

 mature stands it is reasonable to expect that we shall tend to sub- 

 stitute rubber-stamping for tagging. The practice of tagging has 

 become so well established here, however, that the substitution of 

 rubber-stamping cannot be expected to take place quickly. 



No really adequate rubber stamps for use on trees have yet been 

 developed in this country. The requirements for a rubber stamp 

 to be used on trees are a soft spongy rubber, plain numerals, and a 

 base and handle firm enough to withstand hard usage. The rubber 

 base should be set into the wooden base, which at the thinnest part 

 should not be less than half an inch thick. The handle and wooden 

 base should preferably be in one piece, and of some hardwood such 

 as maple. The numerals should be about 2 inches high, and should 

 be narrow for their height. 



In this country great difficulty is experienced, also, in procuring 

 paint of the right quality for rubber-stamping. The paint must be 

 lasting, must be of such consistency as not to run, and must be 

 obtainable in small quantities for field use. In the Northeast a high- 

 grade spar enamel has been found to possess some of the desired 

 characteristics. For immediate use, the enamel should be slightly 

 thickened with pure French zinc powder or by exposure to the air. 

 The thickening can be hastened by spreading the enamel out in a 

 shallow pan. Enamel of the proper consistency does not run when 

 applied to the tree. 



Almost any intelligent common laborer can do a fair job of 

 painting, stenciling, or rubber-stamping numbers on trees. In fairly 

 dense stands, it should be possible to paint or stamp about 100 trees 

 per hour. 



A tree-numbering method recently developed by forest entomolo- 

 gists, makes use of a paint gun with a fine nozzle. Compressed air 

 for this gun may be developed in back-pack pumps such as are used 

 in fighting forest fires. The paint is held in a mason jar attached 

 to the gun. This method has many advantages : The fine spray is 

 forced into all the cracks and crevices of the bark, so that bark 

 smoothing is unnecessary; the numbering can be done freehand 

 and very rapidly; the size of the letters can easily be adjusted to 

 the size of the tree; and the work can be done by relatively inex- 

 perienced laborers. It is important that the paint be kept in a 

 highly liquid state and free from any material that would clog 

 the nozzle. 



PROCEDURE IN NUMBERING TREES 



The numbering of trees on any sample plot should be systematic. 

 It should begin at a corner and proceed back and forth across the 

 plot in rather narrow strips. A separate series of consecutive 

 numbers should be used on each plot, and when any numbers drop 

 out of the series that fact should be recorded. 



