Performance of a Hot-water Apparatus. 147 



are carried to, deposited, and further prepared in, the cells of 

 the bark ; and there become the origin of the new layers, and 

 of the "convergent" (formerly the divergent or medullary) 

 processes. Finally, that other portions of the elaborated fluids 

 are carried down through the cellular tissue of the bark, by 

 the agency of the descending electric current, and form those 

 rootlets which are always protruded at a period coincident 

 with the developements of the buds and foliage. 



I am, Sir, yours, &c. 

 Feb. 1832. G. I. T. 



In the Magazine of Natural History, vol. iv. p. 542., a theory is exhibited 

 which attempts to account for the ascent and circulation of sap in the follow- 

 ing manner : — " The sap, in its ascent in the stem, becomes deprived of 

 some of its constituents, more especially of its aqueous part : this deprivation 

 is effected by the vital principle of the plant decomposing the aqueous parts, 

 and assimilating the resulting gases to its own contituents. As the assimi- 

 lation takes place, a partial vacuum is formed by the change of gases to a 

 solid form ; and this vacuum is immediately filled with sap rushing into it, 

 according to the well-known law of the tendency of fluids to rush into any 

 cavity deprived of the presence of air." 



In a subsequent number of the Magazine of Natural History (No. xxiv., 

 or vol. v. p. 197.) this theory is thus criticised by a correspondent: — 

 ** As the sap must have ascended once before this theory can come into 

 operation, I want the author to explain what is the cause why the sap 

 rises in the first instance into the upper part of the stem. What impulse 

 forces or drives it up primarily, in order that, when it has ascended, the 

 process of assimilation, &c, vacuum, and renewed supply, may take place 

 in the manner the above theory supposes ? When the author of the theory 

 has given this explanation, I shall rest satisfied ; but in doing this, he will, 

 I apprehend, be under the necessity of subverting his own theory, as it 

 occurs to me, that the cause which produces the first rise of sap will 

 suffice to account for its subsequent ascent." 



Art. VI. Observations made on the Performance of a Hot-'water 

 Apparatus in a Pinery at the Earl of Egremont' s, Petlvortk, Sussex, 

 during the severe Weather in January last, by Mr. Harrison, the 

 Gardener there. Communicated by Mr. Cottam. 



The pinery is 60 ft. long, and 12 ft. wide. It is 12 ft. high 

 at the back, and 5 ft. in front ; the boiler is 2 ft. in diameter ; 

 the quantity of water in the boiler and pipes is 160 gallons. 



A small fire was made each day at three o'clock in the 

 afternoon ; a little more fuel was added at six and nine o'clock ; 

 and nothing more was done to the fire until the next day, at 

 three o'clock in the afternoon. The quantity of coal con- 

 sumed is less than one third of what was used when the com- 

 mon flues were employed. According to the present system, 

 the whole of the water (160 gallons) is in circulation twenty- 



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