Lntroductory. 15 
14. Reserve Food. Active protoplasm may absorb 
nourishment in excess of immediate requirements and hold 
it as reserve food. In plants, this reserve food is in the form 
of starch, sugar or oil; in animals it is in the form of fat. 
These substances are formed by the protoplasm from its 
crude food materials through a process known as assimila- 
tion (59). The reserve food enables the plant or animal to 
live through limited periods of scarcity, and to meet the de- 
mands necessitated by reproduction (16). 
15. Growth is the permanent change in form of a living 
vegetable or animal body, and is usually accompanied by in- 
crease in size. It may occur either through increase in size 
of cells already formed, or through cell multiplication. The 
latter may take place either by division of older cells into 
two or more smaller cells (Fig. 1), or by the formation of 
new cells within older ones,— the young cells thus formed 
attaining full size by subsequent expansion. 
16. Reproduction is the multiplication of living indi- 
viduals. It is one of the properties of protoplasm. As 
living cells containing protoplasm multiply by forming new 
cells, so living beings, which consist of cells, multiply by 
the separation of a part of their own cells, and this separa- 
ted group of cells grows into a complete organism like the 
parent. The higher plants multiply by seeds (156), which 
are separated from the parent plant, and each of which con- 
tains a young plant already formed within it (54). The eggs 
from which young birds are hatched contain cells filled with 
living protoplasm, and the protoplasm of the living young 
of mammals is separated from the parent before birth. 
17. Reproduction is either Sexual or Non-Sexual. 
Sexual reproduction can take place only upon the union of 
