14 



Now whether we adopt method a, |3 or y, we 

 may obtain the contents of the sample trees 

 either (1) by felling them and measuring 

 them accurately, or (2) by estimating their 

 contents standing. lu either case, we may 

 seek to ascertain one of two things : (i) the 

 total solid contents of the trees, or (ii) sepa- 

 rately the quantity of each class of wood 

 or timber in them. 



b. By means of the ric^-height. 



c. With the help of specially prepared tables of 



volumes (volume-tables) or of form-factors. 



II. VALUATION WITHOUT ANY MEASUREMENTS (eye survey). 



A. Ocular estimate, after observation either (a) of the 



whole crop, or (b) of sample plots. 



a. Of the number of stems of different size-classes. 



b. Of volume of material (1) per acre, or (2) 



standing in the whole forest. 



B. Estimate based on examination of figures given in 



existing yield-tables prepared either 



a. Specially for the locality, or 



b. For the forest district or region. 



2. Choice between Complete Survey and Survey by Sample Plots. 



The valuation survey of a crop by means of sample plots obvious- 

 ly requires very much less labour and time than a complete survey, 

 and must therefore be adopted whenever it is likely to fulfil the 

 objects of the survey. Its admissibility depends on three principal 

 considerations : 



I. THK PUKPOSK OF THK SURVEY AND THB DEGREE OF ACCURACY 

 DKUANDKD The object of a survey is not necessarily always 

 to ascertain the total contents oi the crop : we may desire 

 to know only how much material on an average there is on 

 an acre, or we may seek to obtain figures required for the com- 

 pilation of certain tables, or we may simply wish to determine 

 the quality of the soil br locality, and so on. In all these 

 latter cases the survey of well-s'elected plots, the area of which 

 has been accurately measured, is preferable to the survey of 



