172 Mr. E. H. Acton. The Assimilation of Carbon 



~No. 12. Experiments with " Extract of Natural Humus.'" 



An extract of " humus " was obtained by digesting the soil — a ligbt 

 leaf mould — -with dilute alcohol on a water-bath for eight hours and 

 filtering through asbestos and powdered glass. The alcohol was dis- 

 tilled off on a water-batb, the residual solution diluted with water, 

 and again filtered as above. 100 c.c. of this solution evaporated to 

 dryness at 110° C. left 0'3708 grain of solid residue, which showed 

 on combustion that it contained 15 per cent, of carbon.* 



As bacteria, fungi, algae, &c, rapidly make their appearance when 

 such a solution is allowed to stand, I found it convenient to keep the 

 alcoholic extract, referred to above, and evaporate off the alcohol just 

 before use. 



~No. 12. — Experiments with " Extract of Natural Humus." 

 A. With Cut Branches. 



Solution used. 



Plants, 



Kesults. 



I. Culture solution 

 + 20 c.c. of the 

 " extract " 



II. Ditto 



Scrophularia aquatica 

 Tilia Eurojpcea 

 Phaseolus vulgaris 

 Cheiranthus Cheiri 



iVo formation of starch 

 (6 days). 



No starch (8 days). 



B. Solution supplied to the B,oots. 



Same solution as 

 above 



Acer pseud oplatanus (2 plants) 

 Quercus rpbur (2 plants) 

 Phaseolus vulgaris (1 plant) 

 Cheiranthus Cheiri 



Starch was formed in the 

 leaves, but in all cases 

 only a small quantity 

 after 6 days (not tested 

 earlier) . 



* The residue contains a small quantity of nitrogen, but the amount varies 

 greatly in different extracts. 1 have not experimented with any extract of 

 " natural" humus perfectly free from N (compare Exp. No. 13). 



