112 ANIMAL LIFE 
Such are the pitcher-plants and sun-dews, and Venus-fly- 
traps, which catch insects and use them for food nutrition. 
But there are many plants, the fungi, which are not green 
—that is, which do not possess chlorophyll, the substance 
on which seems to depend the power to make organic 
matter out of inorganic substances. These plants feed on 
organic matter as animals do. The cells of plants (in their 
young stages, at least) have a wall composed of a peculiar 
carbohydrate substance called cellulose, and this cellulose 
wis for a long time believed not to occur in the body of 
animals. But now it is known that certain sea-squirts 
(Tunicata) possess cellulose. It is impossible to find any 
set of characteristics, or even any one characteristic, which 
is possessed only by plants or only by animals. But nearly 
all of the many-celled plants and animals may be easily 
distinguished by their general characteristics. The power 
of breaking up carbonic-acid gas into carbon and oxygen 
and assimilating the carbon thus obtained, the presence of 
chlorophyll, and the cell walls formed of cellulose, are char- 
acteristics constant in all typical plants. In addition, the 
fixed life of plants, and their general use of inorganic sub- 
stances for food instead of organic, are characteristics 
readily observed and practically characteristic of many- 
celled plants. When the thousands of kinds of one-celled 
organisms are compared, however, it is often a matter of 
great difficulty or of real impossibility to say whether a 
given organism should be assigned to the plant kingdom 
or to the animal kingdom. In general the distinctive 
characters of plants are growped around the loss of the 
power of locomotion and related to or dependent upon it. 
67. Living organic matter and inorganic matter.—It would 
seem to be an easy matter to distinguish an organism—that 
is, a living animal or plant—from an inorganic substance. It 
is easy to distinguish a dove or a sunflower from stone, and 
practically there never is any difficulty in making such dis- 
tinctions. But when we try to define living organic matter, 
