144 TRANSACTIONS OF ROYAL SCOITISH ARBORICULTURAL SOCIETY. 



the cone bulges to the shape of a paraboloid (Fig. i8, p. 147), 

 the form-factor is larger. On the other hand, with increased 

 volume in the lower part, when the cone tends to the form of a 

 neiloid (Fig. 17, p. 147), the form-factor is smaller. 



II. — Breast-height Form-factor with Timber 

 Measurement to the Tip. 



Here the base is at 4 ft. 3 ins. above ground, and the form- 

 factor expresses the ratio between the volume of the whole tree 

 to the tip and that of a cylinder of the same base and height. 



r.q 1 



F.<i2 



r,(; 3. 



Fig. 3 shows a very small tree not yet 4 ft. 3 ins. in height. 



Since there is a slight volume but no basal area, the ratio 



V V . 



rr ; — ;; r— -:— — - = — = Infinity. The form-factor is at 



Basal Area x Height o 



Infinity. Fig. 4 shows a small tree 8 ft. 6 ins. in height. Let 

 us assume, though they are probably not mathematically 

 exactly equal, that the surplus of timber below breast-height is 

 equal to the deficiency, within the cylinder, above. On this 

 assumption it is obvious that the volume of the tree equals that 

 of the cylinder. The form-factor is, therefore, i"ooo. Fig. 5 

 shows a slightly larger tree. Here the surplus does not 

 neutralise the deficit completely. The form-factor has, there- 

 fore, decreased somewhat, say from i-ooo to "600. Fig. 6 

 shows a relatively large tree in which the difference between 

 the basal area at breast-height and that at the ground is small. 



