1889.] Carbon by Green Plants from Organic Compounds. 121 



"extract of natural humus," the "humus-like" product obtained by 

 the action of alkalis on saccharon. The results of these experiments 

 may be tabulated as follows : — 



Starch is formed when the compound is supplied either directly to 

 the shoots or through the medium of the roots, with glucose, sac- 

 charon, glycerin,* inulin.f (A. Meyer's observation for " supplied to 

 shoots.") 



Starch formed when compound is supplied directly to the leaves, 

 but not when supplied to the roots, with " soluble starch." 



Starch formed when compound is supplied to the roots, but not when 

 directly supplied to the leaves, with " extract of natural humus." 



Starch not formed at all from acrolein, acrolein-ammonia, com- 

 pound of acrolein with NaHS0 3 , allyl alcohol,* aldehyde, aldehyde- 

 ammonia, dextrin, glycogen, la3vuiinic acid, calcium lsevulinate, 

 " artificial humus substance." 



That glucose is more readily taken up by the roots of plants from 

 0'5 per cent, solution than saccharon. 



That the roots of plants can withdraw all the glucose from a 1 per 

 cent, solution if they be left in the solution for a sufficient length of 

 time, and the plants remain healthy. 



The conclusions I should draw from these experiments are : That 

 green plants cannot normally obtain carbon for assimilation from 

 organic substances except carbohydrates or closely related bodies, not 

 from aldehydes or their derivatives, and not even from all carbo- 

 hydrates. 



That a compound may be a source of carbon when supplied to the 

 leaves but not when supplied to the roots, and vice versa. 



That green plants, owing to the normal process of obtaining carbon 

 being from C0 2 , have, to a large extent, lost the power of using 

 organic compounds as a source of carbon. (Parasitic and saprophytic 

 plants, especially fungi, undoubtedly do always obtain their carbon 

 from complex organic compounds.) 



That many (? all) green plants behave in the same manner towards 

 the substances enumerated as regards formation or non-formation of 

 starch. (Contrast in this respect with fungi, which are often charac- 

 terised by decomposing special substances.) 



That if a single substance of an aldehydic or ketonic nature is 

 formed by plants as an intermediate product between C0 2 and H 2 

 and glucose (or starch), it can only be polymerised by the plant under 

 special conditions, probably at the moment of formation. 



* When glycerin was supplied to the roots in solutions stronger than 10 per cent, 

 starch was not found, 

 f Vide note above. 



