152 MORPHOLOGY, EVOLUTION, AND CLASSIFICATION 



the basis for the established belief in the evolution or develop- 

 ment of the higher plants and animals from simpler forms. 



188. Classification. The classifications of animals and plants 

 are attempts to express the actual kinships, or what among 

 human beings are called blood relationships, which are believed 

 to exist among them. To illustrate the principles of classifica- 

 tion let us consider the position of the pines among plants. All 

 of the pines have for their fruit a scaly cone whose seeds are 

 borne naked at the base of each scale and mature the second 

 year. The leaves are needle-shaped, evergreen, and clustered. Any 

 tree which has all the characteristics above given is a pine. 



The spruces, hemlocks, firs, and larches agree with the pines 

 in many respects, but all of them mature their seeds the first 

 year, and their foliage is different. The American cypress has a 

 globular woody cone and deciduous leaves in two rows. Th 

 arbor vitse and the juniper have awl-shaped or scale-like leaves, 

 not in clusters. 



All of these cone-bearing trees are distinct kinds, but they 

 are grouped together because the seeds are borne naked on the 

 scales of the cones. This peculiarity separates the group from 

 a much larger assemblage of seed plants in which the seeds 

 are borne inclosed in seed cases, pods, or other types of fruit. 

 Finally, all of the seec?-bearing plants are separated from the 

 spore-bearing groups by the possession of methods of repro- 

 duction which develop seeds. 



Thus the pines find their place in the classification of plants 

 through clearly marked characters which define several different 

 groups. These characters are (1) the presence of the seed, (2) the 

 fact that the seeds are exposed or naked, (3) the development of 

 the seeds in a cone type of fruit, and finally (4) some peculiar- 

 ities of the cone, and the character of the foliage. The process 

 of classification leads from an assemblage of more than one 

 hundred thousand kinds of plants (the seed plants), through 

 successively smaller divisions, to the relatively small group of 

 the pines, with hardly more than seventy known kinds. 



