CLEAEING THE CROP 161 



the instrument is given a slight turn, when the rod catches 

 in a toothed plate on which there is a scale of heights. 

 Both these instruments fold up into a small space and 

 can be carried in a pocket. 



The centre J girth or the diameter can be judged direct 

 or arrived at in either of the following ways : 



The measurements may be taken at breast height and 

 an allowance made for the taper of the tree, or they may 

 be taken at breast height and the length taken to where 

 the I girth is judged to be — say 3 inches. The two | 

 girths are added together and divided by 2, to find the 

 mean | girth. 



Measurements of Whole Woods. 



This can be done by — (1) Measurement of all the trees; 

 (2) measurement of sample trees; (3) measurement of 

 sample plots. 



By the first method, which can only be practised on 

 small areas, or where there are several species and where 

 the trees vary greatly in size, they are measured according 

 to the methods explained above, and the totals of each 

 class computed at the end. 



When the area is large, the other methods are much 

 quicker and quite as accurate. 



When measuring sample trees, all the trees are counted 

 and a number of trees over the whole area measured. 

 From these figures the average stem is found by dividing 

 the total number of cubic feet in those measured by their 

 number. The figure for the average tree is multiplied 



11 



