ABSORPTION OF FOOD MATERIALS 135 
the parts played by the root and the fungus or bacterium 
respectively are not at all determined. The atmospheric 
nitrogen apparently is made to enter into some form of 
combination, and is then absorbed by the root, probably 
through the tissue of the fungus. It is not absorbed by the 
leaves of the plant. 
Organic compounds of nitrogen are seldom presented to 
the roots of plants, so that the amount of the element which 
is absorbed in such a way is very small. Indeed it may 
be said that such an absorption is almost entirely excep- 
tional. It has been found that plants are able to utilise 
urea and other amides when those are present in the soil. 
In very rich soils, or those containing a large quantity of 
humus, such compounds are to be met with, and there is a 
probability that they are more easily worked up into actual 
nutritive substance than the inorganic compounds which 
have been spoken of. 
A few plants obtain a more fully elaborated material in 
a very different way. These are the so-called insectivorous 
plants, which have the power of utilising protein substances. 
Among them may be mentioned the pitcher plants, 
Nepenthes, Sarracenia, &c., and the fly-catching plants, 
Drosera, Dionea, and others. In the pitchers of Nepen- , 
thes, &¢., which are specially modified foliar structures, 
there is an accumulation of water, in which insects are 
from time to time drowned. Their bodies decay, or are 
digested by a peculiar secretion, which is prepared in the 
tissue of the pitchers, and excreted into the water they 
contain. The products of the decomposition or digestion 
are absorbed by the tissue of the pitchers in the same way 
as similar products are absorbed by the stomachs and 
intestines of animals. Drosera and Dionea bear certain 
glandular structures on their leaves which pour out a fluid, 
by which insects become surrounded after alighting on 
the laminw. This secretion possesses digestive properties 
resembling those of the gastric and pancreatic fluids of 
animals, and by the action of this juice the bodies of the 
