THE CELL 21 
and carbon dioxide from the air. In the process of photosynthesis, 
sugar is manufactured from the carbon dioxide and some of the 
water. This sugar may be stored in the cells or changed into 
some other form of stored food ; or it may combine with elements 
from the soil and be stored as food; or it may become incor- 
porated in the protoplasm. Substances which are very different 
from protoplasm are thus taken into the protoplasm and then 
combined and made into protoplasm. 
2. Metabolism. The sum of the processes of chemical change, 
including the building up and oxidation of material within the 
protoplasm, is known as metabolism. One of the activities of pro- 
toplasm is the combining of sugar with elements from the soil to 
produce proteins which become a part of the protoplasm. ‘This 
is a constructive process. Destructive processes also take place 
in the cells of plants as complex compounds aré broken down 
with the liberation of energy. The protoplasm uses this energy 
in various activities. 
3. Growth and reproduction. The growth of protoplasm is 
due to changes within the protoplasm, while the growth of non- 
living things, such as ordinary crystals, is accomplished by the 
addition of layers on the outside. Reproduction is essentially 
the separation and growth of small portions of protoplasm de- 
rived from one or two parent organisms. Reproduction, there- 
fore, is a form of growth. 
4. Movement. Protoplasm has the power of moving and is 
frequently in motion. This motion of the protoplasm in a cell 
can be easily seen with the aid of a microscope. In some cases 
the motion is evident as an active streaming, while in others it 
manifests itself by changes in the shape and position of the 
protoplasmic masses. Fig. 12 shows three drawings, made at 
fifteen-minute intervals, of the same cell. The changes in the 
arrangement of the protoplasm are very evident. Protoplasm 
not only possesses the property of moving but it may also cause 
the motion of whole organs or even organisms. This kind of 
movement is more evident in the case of animals than in plants, 
but is easily recognized in the case of sensitive plants and in 
