PART III 
STRUCTURE AND LIFE HISTORIES 
CHAPTER XII 
LIFE HISTORY OF A FERN 
139. Morphology. In the preceding chapters we con- 
sidered various physiological processes, the primary 
result of which was to maintain the life of the individual 
plant. Most of those processes are carried on by all 
plants. Every one knows, however, that plants differ 
widely from each other in both structure and habit of 
life. In other words, we recognize the fact of variation. 
This means that different plants solve the same problems 
of life in different ways. For example, some plants expose 
a large amount of chlorophyll to sunlight by forming thin 
leaf-blades of relatively large area; while others, such as 
the cactus, accomplish the same result by developing 
thick, succulent green stems, and dispensing with leaves 
entirely. Some leafy plants raise their foliage up to the 
light on strong woody stems, able to stand alone; while 
others secure this result by climbing up on other plants. 
In many cases the organs of plants are disguised, appear- 
ing to be what, in reality, they are not; stems may mas- 
querade as leaves, and leaves as stems. That phase of 
botany which concerns itself with a comparative study of 
structures, and seeks to interpret the real structural 
