CHAPTER I 

 INTRODUCTION 



Morphology deals with the form and structure of plants. It is con- 

 cerned with both gross, external features and minute, internal details. 

 It includes a study of the development of plants throughout all their 

 growth stages, called ontogeny, as well as their evolutionary development, 

 or phyJogeny, by means of which all existing plants have been derived from 

 those of past ages. Morphology considers the interrelationships of the 

 groups forming the larger units of classification, but does not deal with 

 species, the study of which belongs to taxonomy. One of the main objec- 

 tives of morphology is the determination, so far as possible, of lines of 

 descent. 



A sound knowledge of the structure and development of plants is a 

 necessary foundation for successful specialization in any phase of botany, 

 whether it be taxonomy, physiology, ecology, pathology, or genetics. 

 A study of the lower plants is often neglected, since the higher ones are 

 more famihar and, in general, more important. Many of the problems 

 encountered in the higher plants, however, are more easily studied in 

 the lower plants, whose structure and functions are much simpler. The 

 logical procedure is to study simple plants before attempting to under- 

 stand complex plants. 



CLASSIFICATION OF PLANTS 



For many years the system of classification most widely adopted by 

 botanists has been one in which the plant kingdom is separated into four 

 major divisions: Thallophyta, Bryophyta, Pteridophyta, and Spermato- 

 phyta. Each division comprises a number of classes. A class is made up 

 of orders, an order of Jamilies, a family of genera, and a genus of species. 

 Categories of intermediate rank are designated by the prefix suh. 



At one time the two subkingdoms Cryptogamia and Phanerogamia 

 were recognized, the former including the three lower divisions and the 

 latter the fourth division. These names have fallen into disuse because 

 they are inappropriate. Cryptogam means "fertilization concealed" and 

 phanerogam means "fertiUzation evident." The names were given 

 because stamens and pistils, the organs once thought to produce directly 

 the cells which unite in fertilization, are present in seed plants but not in 

 plants without seeds. After the true nature of fertiUzation was dis- 



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