HOMOLOGY AND ANALOGY 



237 



rV. The Spermatophytes (Gr. sperma, seed), or seed-bearing plants, include 



two groups, as follows : 



The Gym'nosperms (Gr. gymnos, naked), or naked-seed-bearing plants, are a 

 small group related to the ferns on one side and the flowering plants on the other. 

 Two classes are found: the cy'cads, of which the so-called "sago palm " is 

 an example, and the co'nifers or evergreens, as pines, spruces, firs, hemlocks, 

 cypress, and others. The evergreens include the sequoias, the largest and 

 oldest trees. There is a total of only about 450 species of gymnosperms. 



The An'giosperms (Gr. an- 

 geion, case or vessel), or true 

 flowering plants, are a very 

 large group, including all of 

 our common grasses and grains, 

 our flowering trees and shrubs, 

 and flowering plants. There 

 are more than 140,000 known 

 species. 



The total number of known 

 species of plants is more than 

 240,000. 



Homology and Analogy. 



— In the classification of 

 plants and animals, there 

 is one underlying principle which is used to show relationships. 

 Plants which have similar structures in similar parts of their 

 bodies are almost certainly closely related to each other. When 

 structures or organs on different animals are found in correspond- 

 ing positions and to be similar in structure, they are said to be 

 homoVogpus. Homology is of great use in determining rela- 



Angiosperms, or flowering plants : a colony of 

 trilliums. (Photograph by W. C. Barbour.) 



Wrisf 



Wrist 



DOLPHIN 



BIRD 



LION 



Compare the external appearance and the bones of the fore appendage of a bat, 

 a bird, a dolphin and a lion. 



