148 
STRUCTURE AND LIFE HISTORIES 
nature of an organ, no matter how it may be disguised, is 
termed the science of form, or morphology. 
140. Life History. Every plant, in the course of its 
existence, passes through a series of changes in orderly 
sequence. Like an animal, every plant begins life as a 
single cell, the egg, or the equivalent of an egg. Except 
in some of the lower forms, the egg develops into an 
FIG. 106. A fern (Anisosorus hirsutus), showing portion of the stem 
above ground. 
embryo, and the embryo matures into an adult. By a 
series of more or less complicated processes the adult 
eventually gives rise to another egg, like the one from 
which it came, thus completing one life-cycle and initiat- 
ing another. These various changes constitute the life 
history of the individual. The various stages of life 
history common to most plants are nowhere more clearly 
