236 HOW CROPS FEED. 
absorb the juices of the roots of trees; such are the beech 
drops (Zpiphegus), pine drops (fterospora), Indian pipe 
(Monotropa); the last-named also grows upon decayed 
vegetable matter. 
The dodder (Cuscuta) 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 érom 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 ¢ the absorp- 
tion of humus by the roots, it remains to speak of its as- 
similation by the plant. One of the indications of this 
assimilation is derived from the absence of the peculiar 
color of humus in the interior of the plant, which has ab- 
sorved a strongly colored solution of humate of potash, as 
compared to the different deportment of coloring matters 
* Dr. Luck (Ann. Chem. u. Pharm., 78, 85) has indeed shown that the mistle- 
toe (Viscum album) decomposes carbonic acid in the sunlight, but this plant has 
greenesh-yellow leaves containing chlorophyll. 
+ We take occasion here to say explicitly that the only valid criticism of De 
Saussure’s experiment on the Polygonum supplied with humate of potash, is 
Licbig’s, to the effect that the solution Jost humic acid to the amount of 43 milli- 
grams not as a result of absorption by the plant, but by direct oxidation. 
Mulder and Soubciran both agree that such a solution could not lose perceptibly 
inthis 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 objection (and he has furnished no proof that his statement is true), then 
De Saussure has demonstrated that humic acid is absorbed by plants, 
