CHAPTER XXI 

 CLASSIFICATION OF PLANTS AND ANIMALS 



Problems : What is meant by a system of classification f 



How are plants classified? 



What is homology f What is analogy f 



How are animals classified f 



Laboratory Suggestions 



A visit to a botanical garden. 



Laboratory exercise. Homologies . and analogies in plants and animals. 



Demonstration. Types which illustrate increasing complexity of body form 

 and of division of labor. 



Museum trip. For the identification of examples of the principal animal 

 phyla. This should be preceded by objective demonstration work in the 

 school laboratory. 



Plants are placed in Groups. — If we plant a number of pea 

 seeds so that they will all germinate under the same conditions of 

 soil, temperature, and moisture, the seedlings will differ one from 

 another in a slight degree. But in a general way they will have 

 many characters in common, as the shape of the leaves, the pos- 

 session of tendrils, the form of the flower and fruit. A species 

 (spe^shez) is the smallest group of plants or animals having certain 

 characteristics in common that make them different from all other 

 plants or animals. Individuals of a species differ slightly; for 

 no two individuals are exactly alike. 



Similar species are placed together in a larger group called a genus 

 (je'nus; plu. gen' era). For example, many species of peas — the 

 wild beach peas, the sweet peas, and many others — are all grouped 

 in one genus (called Lath'yrus, or vetchling) because they have 

 certain structural characteristics in common. 



Genera of plants or of animals are brought together in still 

 larger groups, the classification being based on general likenesses 

 in structure. Such groups are called, as they become successively 



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