103 JOURNAL OF FORESTRY 



tionably wider, and more or less twisted vertically. Within a species 

 the number of measurements vary from 100 to 400 for length and 50 

 to 200 for width, the discrepancy in the figures depending upon the 

 amount of available material. The measurements obtained from mace- 

 rated material were checked by others from permanent mounts of the 

 same specimens which had been prepared previously. No change in 

 cell width was detected in material exposed to the action of the acid 

 for a period of less than 30 hours. If the acid was permitted to act 

 for 48 hours or more, partial disintegration of fiber took place. 



All measurements were made with an ocular micrometer of the 

 usual type which had been previously calibrated from a stage microm- 

 eter. In. computing fiber lengths a 32 mm. micro-tessar objective was 

 used with a lO X eye piece, while fiber widths were measured success- 

 fully with a 4 mm. objective of the usual type. The speed with which 

 measurements can be made depends to a considerable degree on the 

 quantity of fiber on the slide. If the fibers are too numerous in the 

 field of vision, the ends are not readily visible, interfering with accurate 

 measurements. On the contrary, scarcity of fibrous material on the 

 slide leads to delay owing to the necessity for the centering of fibers 

 which happen to be some distance apart. Experience soon taught the 

 amount of fibrous material for optimum results. In general, measure- 

 ments were restricted to fifty or less per mount in order to obviat: to a 

 large degree the possibility of measuring the same fibers two or three 

 times. 



Table 1 indicates the fiber lengths and widths of thirty-three species 

 of dipterocarps . 



An examination of the tabulated measurements lead to a number 

 of interesting deductions. There is apparently little variation in the 

 fiber length of the dipterocarp group as a whole, but individual varia- 

 tions are both striking and significant. Fibers are longest as a rule 

 in the softer members of the family, while the reverse applies in the 

 harder-wooded species. For example, the average fiber length of 

 Anisoptcra spp. is 1.70 mm., Dipterocarpiis spp., 1.77 mm., and the 

 lighter Shorcas such as S. e.vimia, S. palosapis, and 5. teysinanniana, 

 1.76 mm., I.n4 mm., and 1.68 mm., respectively. In contrast to the 

 above, the harder woods of the family are proportionately shorter 

 fibered. Species of Hopea possess an average length of 1.40 mm., 

 Balanocarpus 1.38 mm., Vatica 1.34 mm., and hard Shorcas l.Ki mm. 

 A like variation also exists in the dififerent species of the same genus 



