18 CIRCULAR 3 3 3, U.S. DEPARTMENT OP AGRICULTURE ' 



plot work is to be done in snow. Aluminum paint promises to give 

 satisfaction on trees having a dark bark. 



Posts of durable wood, concrete, stone, iron pipe, reinforcing steel, 

 or angle iron may be used to mark the permanent stations on sample 

 plots. They should be so firmly set in the ground that frost cannot 

 heave them. Lengths of angle iron, since they nest together, can 

 be packed more easily than round pipe. Angle iron used alone 

 sometimes is badly affected by frost heaving. To avoid this, a 

 small plate 6 or 8 inches wide may be riveted or otherwise fastened 

 to one side of the angle bar close to the lower end. When this plate 

 is driven into the soil it usually holds firmly. If one plate is inade- 

 quate, a second plate should be fastened on the other angle. Rein- 

 forcing steel cut to proper length is especially useful for subplot 

 corners. In loose soils an iron post can be anchored more firmly 

 if the end to be set in the ground is bent into an L or a J, or 

 perforated and fitted with an iron crossbar. To be conspicuous, 

 posts should overtop ordinary weeds and grass and should be painted 

 a bright color. Wooden markers should be protected from fire by 

 stones or dirt piled at the base. 



Specifications for a concrete post suitable for use as a sample- 

 plot marker are as follows : 



Use 1 part Portland cement, 2 parts clean sharp sand, and 3 parts clean 

 gravel or crushed rock that will pass a %-inch screen. Only so much 

 water should be used that the mortar will completely coat the coarser ma- 

 terials, that all the particles of the aggregates will adhere, and that, when 

 the concrete is tamped, the water will just flush to the surface without quak- 

 ing. Concrete should be thoroughly mixed (preferably for iy 2 minutes in a 

 concrete mixer) and tamped in form. Inside of form should be smeared 

 with oil or grease (old engine oil is suitable) before concrete is poured. For 

 reinforcing, ^-inch deformed reinforcing rod 23 inches long should be used. 

 Post should be cast upside down, by placing cap, tied to reinforcing rod, face 

 down in form and pouring concrete into larger end of form. Outside surface 

 of post should be smooth. Post should be allowed to remain in form 24 hours, 

 and after removal should be kept moist for 1 week while curing. The form 

 should be thoroughly cleaned after each casting. 



A post made according to these specifications is shown in plate 

 4 and figure 1. 



If a corner falls upon rock and it is impracticable to choose 

 another location for the line, the corner point should be scratched 

 or chiseled deeply in the stone and suitable reference or witness 

 markers established. 



Several different methods of marking plot corners are illustrated 

 in plate 4. 



Plot corners should be marked with the plot and corner numbers. 

 This inscription should preferably be painted on the corner post. 

 It may be stamped on a tag and wired to the post. On a wooden 

 post it may be scribed, carved, or outlined with nails, and the direc- 

 tions of adjacent boundary lines may be indicated by a cross on 

 the top. One corner of each subplot should bear the subplot number. 



The markers for each class of station should be distinctive. Those 

 for plot corners should be the most prominent. Other stations may 

 be denoted with smaller markers, each series of which is differen- 

 tiated from the others by the use of different-colored paint or dif- 

 ferent symbols. Confusion among the various types of markers 

 can be avoided by properly locating and indicating them on the 

 plot map. 



