PART HI 



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 



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