158 



PLANT BIOLOGY 



called biennials (Latin, bi = two -\-annus = year). Perennials 

 are plants that live year after year. Hollyhocks and dahlias, 

 for instance, store food in fleshy roots year after year, while 

 the parts above ground die, as in the case of beets and carrots. 

 Other perennials, like trees and shrubs, lose only their leaves 

 at the end of each season. 



167. . Deciduous and evergreen trees and shrubs. Trees 

 and shrubs may be classified as evergreen or deciduous. Since 

 the leaves of pines, spruces, and hemlocks remain green and 

 attached to the stem during the winter, these plants are known 

 as evergreens. Certain shrubs (rhododendrons, arbutus, and 

 wintergreen, for example) also keep their green leaves 

 throughout the winter, and so in a sense they may be regarded 

 as evergreens. Maples, elms, and horse-chestnuts, on the 

 other hand, shed their leaves in autumn ; they are therefore 

 said to be deciduous (Latin, de = from-}-cadere = to fall). 



168. Field work on plant classification. Optional. No. 64. 



If possible, teachers should accompany their pupils on a field trip, 

 point out and name the plants best adapted for a study in classifi- 

 cation, using perhaps an outline like the following: 



II. SCIENTIFIC METHOD OF CLASSIFICATION 



169. Scientific classification of plants. The various 

 methods of grouping plants that we have thus far considered 

 do not indicate real relationships among plants, for these 

 schemes call attention only to certain superficial resemblances 



