Dixon and Marshall — Examination of the Wood of Trees. 365 



The fresh wood of Fopuhia alba taken in November was very dnj, and 

 had a small specific gravitj' ; accordingly the amount percolating through a 

 piece of stem having a cross-section 1 sq. cm. is very different in a fresh and 

 in an injected specimen. Throtigh tlie former 0-158, and through the latter 

 0-285 g., passed through under unit head per sq. cm. per minute. 



Tablk V. 



Popidus alba. 



From Table V we see the average cross-section of the upward streaming 

 protoplasm of the cells is 0-049 sq. em. In this we would require a move- 

 ment having a velocity of 3-220 cm. per minute, to overcome the leak of 

 the fresh stem or, 5-825 cm. per minute, to counterbalance the leak of the 

 injected stem. 



Two other determinations were made on the wood of Pojmlus alba. In 

 them two adjacent portions («) and {b) of the same branch were used. They 

 were prepared from the branch on the day after it had been cut from the 

 tree. Meanwhile the branch had lain exposed to the air. Owing to this 

 circumstance, it was to be expected that the experimental cylinders would 

 contain comparatively large quantities of air. The first woody cylinder («) 

 had an effective cross-section {i.e. omitting pith and stained heart wood) of 

 4-12 sq. cm., and before injection transmitted 0-177 g. per minute, or 0-043 g. 

 per sq. cm. per minute. To make good this percolation, protoplasmic 

 streaming in the cells having a velocity of 0-876 cm. per minute would be 

 required. When injected («) transmitted 0-210 g. per sq. cm. per minute, 

 necessitating a velocity of 4-289 cm. per minute for the protoplasm. In the 

 case of the cylinder (5) the rate of leak before injection was 0-083 g. per 

 sq. cm. per minute ; after injection, this rate became 0-277 g. per sq. cm. per 

 minute. The protoplasmic velocities in the cells necessary to overcome these 

 would be 1-687 cm. per minute, and 5-654 cm. per minute respectively. 



Of the stems examined by us that of a Prunus — unfortunately the species 

 was not recorded — showed the smallest proportion of cells in the cross-section. 



SOIENT. PKOC. R.D.S., VOL. XIV., NO. XXIX. 3 N 



