NOTES AND QUERIES. 317 



found weights one-fourth greater for spruce and one-seventh 

 greater for Scotch pine. 



After giving figures to indicate the air-dried weight of the 

 dead covering produced annually by the fall of leaves and other 

 vegetable debris in forests of various species and ages, the author 

 states that, according to M. Henry's weighings, at the end of one 

 year, a weight of 100 lbs. of oak and hornbeam leaves produces a 

 gain of at least •666 lb. of nitrogen. The leaves have by that time 

 lost their coloui", but not their form, and are far from being 

 reduced to humus. Their action as gas-absorbers is slowed down, 

 but only ends with their complete decomposition. This takes 

 three years for certain common species such as beech, and nearly 

 twice as long for pine needles. It is thus a very moderate 

 estimate to say that, after allowing for all losses of gas returned to 

 the atmosphere during the process of decomposition, there still 

 remains "850 lb. of nitrogen absorbed and fixed from the air by 

 each 100 lbs. of dead leaves. This quantity is pure profit — the 

 increment of the leaves from the moment they fall to the ground. 

 But at the time of falling they contain a certain quantity which 

 amounts to over 1 per cent, for the principal species. This 

 may be considered as the minimum for oak, beech and hornbeam. 

 The total loss of nitrogen resulting from the bui'ning of the leaves 

 is therefore 1*850 lbs. per 100 lbs. of dry leaves of these thi-ee 

 species. Probably it is at least 2-500 lbs. for pine, but for safety 

 it may be taken as 2 lbs. 



Debris. 



The dead twigs, etc., etc., which reach the ground are also nitro- 

 genous compounds. They decompose more or less slowly, but 

 always end by conversion into substances useful to plants (such as 

 starches, nitrates, ammoniacal salts). A fire, even a slight one, 

 destroys these small organs and dissipates the nitrogen, which 

 exceeds '1 per cent. 



Under normal conditions the nitrogen derived from the two 

 above-mentioned sources would have contributed to the formation 

 of ulmic compounds and humus incorporated in the vegetable soil. 

 A fire dissipates it in pure loss The damage corresponds to the 

 price of a manure contaitung the same pr-oportion of the gas. In 

 the case of a hectare of high beech, aged 100 years, the loss of the 

 soil covering would, on certain assumptions, amount to over £2, 16s. 

 per acre. Similarly, in the case of a -tO-year old pine forest, the 



