'>^Z CHEMICAL PROCESSES IN THE PLANT. 



light has no influence at all on the formation of asparagin, but has upon its transform- 

 ation into albuminous substances ; it therefore accumulates in plants germinating 

 in the dark, and remains unaltered till their death. The influence of light can however 

 only be indirect, as is shown by the fact that in Tropaeolum asparagin is formed tempo- 

 rarily in the dark during the first stages of germination, and then again disappears ; and 

 even in Leguminosae appears to undergo subsequent metamorphosis into albuminous 

 substances. The explanation is now quite simple. 



' The following numbers show the percentage composition of asparagin, and the 

 composition of an amount of legumin, containing an equivalent quantity of nitrogen. 



Asparagm. Legumin. 



C = 36"4 G = 64'9 



H- 6-1 H= 8-8 



N = 2I*2 N = 21'2 



= 36-4 = 30-6 



' It is seen at once that in the formation of asparagin out of legumin a large quantity 

 of carbon becomes available. The exact mode in which this comes to pass must be 

 left in doubt, like the fixation of carbon in the re-formation from asparagin of albu- 

 minous substances (albumin is probably formed, and not legumin ; their composition 

 does not vary greatly, but the latter gradually disappears almost entirely in growing 

 plants). But when a plant growing in the dark uses up its non-nitrogenous reserve- 

 material, and even the carbon and hydrogen set at liberty by the conversion of legumin 

 into asparagin, the material which would be produced in the light by assimilation is 

 wanting for the re-formation of the albuminous substances out of asparagin. In 

 Tropaeolum, where asparagin occurs only in the first stage of germination, it may com- 

 pletely disappear in the dark. The amount of asparagin formed is however only 

 moderate, and it disappears before the reservoir of reserve-material is exhausted ; it 

 therefore at most always plays only a subsidiary part, as is also the case in Silybum 

 Marianum, Helianthus tuberosus, and Zea Mais. In Ricinus on the other hand I could 

 not find, either in the dark or in the light, any asparagin at all ; and Dessaignes and 

 Chautard looked for it in vain in the seeds of the gourd, buckwheat, and oat, germi- 

 nating in the dark. Its physiological significance remains therefore at present limited 

 to the Leguminosae ; and in them it is confined to the consumption of the reserve 

 albuminous substances, since it is, according to Pasteur, never present in the flowers. 

 When the lateral buds are put out, this substance is not formed in Leguminosae any 

 more than in other plants. Hartig maintains that the production of asparagin, or at 

 least of a trace of a substance identical with it, is a general phenomenon ; but I think 

 that he had before him the small crystals mentioned above which he mistook for true 

 asparagin. He has moreover not contributed any evidence as to the physiological 

 significance of this substance. 



' The existence of asparagin has also been proved in the leaves and stems of some 

 plants (see Husemann, Pflanzenstoffe) ; and its presence in the underground perennial 

 parts of Stigmaphylloyi jatrophoefoUum almost gives the impression of its being there also a 

 reserve-material.' 



The absorption of assimilated substances into the plant from without takes 

 place in seedlings, the reserve-materials of which are contained in the endosperm, 

 in parasites \ and in saprophytes which contain no chlorophyll. Seedhngs, which 



^ Parasites which contain chlorophyll, like the Loranthacere, can themselves assimilate, and 

 only require therefore to draw water and mineral substances from their host (^see Pitra in Bot. Zeitg. 



