236 tlOW CROPS FEED. 



absorb the juices of the roots of trees ; such are the beech 

 drops {Epiphegus), pine drops (I-^erosporu), Indian pipe 

 {3fo/io(rop(()/ the last-named also grows upon decayed 

 vegL'table matter. 



The dodder ( Ct/scitti() is parasitic upon living plants, 

 especially upon flax, whose juices it appropriates often to 

 the destruction of the crop. 



It is indeed true that there is a wide distinction between 

 most of these parasites and agricultural plants. The 

 former are mostly destitute of chlorophyll, and appear to 

 be totally incapable of assimilating carbon from carbonic 

 acid.* The latter acquire certainly the most of their food 

 from carbonic acid, but in their root-organs they contain 

 no chlorophyll; there they cannot assimilate carbon from 

 carbonic acid. They do assimilate nitrogen from the or- 

 ganic principles of urine ; what is to hinder their obtain- 

 ing carbon from the soluble portions of humus, from the 

 organic acids, or even from unaltered carbohydrates? 



De Saussure, in his investigation just quoted from, says 

 further: "After having thus demonstrated f the absor-p- 

 ti(m of humus by the roots, it remains to speak of its as- 

 similation by the jdant. One of the indications of this 

 assimilation is derived from the absence of the peculiar 

 color of humus in the interior of the ])lant, which has ab- 

 sorbed a strongly colored solution of humate of potash, as 

 compared to the different deportment of coloring matters 



* Dr. Luck (.Inn. C'hem. n. Pharm., 78, 85) has indeed ghown that the mistle- 

 jw ( Visciim album) decomposes carbonic acid in the sunlight, but this plant has 

 greenish-yellow leaves containing ddoroplnjll. 



t We take occasion here to say explicilly that the only valid criticism of De 

 Saussure's experiment on the Polygonum supplied with humate of potash, is 

 Liebig's, to the effect that the solution lost humic acid to the amount of 43 milli- 

 grams not as a result of absorption by the plant, but by direct oxidation. 

 Mulder and Soubeiran both agree that such a solution could not lose perceptibly 

 in this way. That De Saussure was satisfied that such a loss could not occur, 

 would appear from the fact that he did not attempt to estimate it, as he did in 

 the subsequent experiment with water-extract of peat. If, now, Liebig be wrong 

 in his ol)jection (and he has furnished no proof that his statement is true), then 

 De Saussure lim demonstrated that humic acid is absorbed by plants. 



