1098 AGRICULTQRAI, BOTANY, CHEMISTRY AND PHYSIOI.OGY OF PLANTS 



maple which have just fallen, after 4 days' decomposition this content is 

 1.93 per cent and represents about 50 per cent of the total content of humic 

 substance. 



2. • — ^ In the course of the gradual decomposition of freshly fallen 

 autumn maple leaves, the quantity of water-soluble humic substance 

 increases at first and then falls off, a contrary phenomenon to what one 

 would a priori assume, seeing that the source of the humus is not the whole 

 of the vegetable substance, but only some of its particular constituents. It 

 follows from this that it is during. the first period of its decomposition that 

 vegetable residue takes the most active part in the formation of the soil 

 humus. 



3. — The same phenomenon, namely, initial increase followed by sub- 

 sequent reduction of humic substance, is also disclosed in the case of am- 

 moniacal solutions of this substance. These facts prove clearly that humic 

 substance is chiefly formed during the first brief period of decomposition 

 of vegetable detritus. Then, evidently, this substance itself is partly de- 

 composed and passes partly into other forms of humic combinations. 



4. —The ratio between the quantity of water-soluble humic substance 

 and that soluble in ammonia varies with the different leaves undergoing 

 decomposition and the different periods of the process. 



5. — The content of humic substance in decomposing leaves depends 

 on the conditions under which decomposition takes place ; it declines when 

 repeated desiccation of the leaves occurs and to an}^ considerable extent. 



6. — -Although the decomposition of the vegetable residue lasted 100 

 days, the quantity of humic substance formed in the first 8 days was not 

 increased, and after 156 days its solubility in water had completely dis- 

 appeared. 



853 - On the Nutrition of Green Plants by means of Organic Substances. — r.-vvenna 



Cmo, in Atti dclla Reale Accadcmia dei Lrncei, Serie Qitinia, Rendiconfi, Classc di scienze 

 fisichc, matematichc c naturali, Vol. XXY, No. 9, pp. 649-655, ilgs. 3. Rome, May 7, igifi. 



Work carried out in the lyaboratory of Agricultural Chemistry of the 

 Royal University of Bologna. 



In order to ascertain whether plants can live in darkness, provided 

 organic matter is present in their culture medium, maize plants were 

 grown in a sterilised nutrient solution to which glucose had been added in 

 solutions of I, 4, 6 and 10 per cent. One plant without glucose was kept as a 

 control. They were kept for comparison, some in the light, others in darkness. 

 Their growth was observed and they were examined for the presence or 

 absence of starch in their leaves. It was found that even when the plants 

 are imder conditions which enable them to absorb glucose through their 

 roots, no formation of starch takes place in darkness. Further, the most 

 suitable degree of concentration for the glucose seemed to be i to 2 

 per cent. 



In order to ascertain whether the plants treated with glucose had pro- 

 duced starch in their leaves, even in the absence of carbonic acid, a plant 

 in nutrient solution with glucose and a control plant were placed in an 

 airtight glass vessel containing a dish filled with caustic potash. Some 



