176 GROWTH HABITS OF PLANTS 



plant growth and various combinations of factors may produce 

 essentially the same growth-forms. The measurement of any single 

 climatic factor or group of factors, therefore, does not give us an 

 accurate estimate of the value of the climate for plant life. 



For these reasons it was felt by Raunkiaer that the plants them- 

 selves should be the recorders of the biological value of any climate. 

 The factor that was selected was the nature and degree of protection 

 of the perennating bud or shoot apex during the critical season. A 

 perennating bud is one that lives through a critical season and may 

 develop into a shoot during the next growing season. It was neces- 

 sary first of all, therefore, to classify plants on the basis of bud pro- 

 tection. The classification as finally used by Raunkiaer is as follows, 

 the symbol used for each life form following the name in parentheses. 



1. Stem succulents (S). 



2. Epiphytes (E). 



3. Megaphanerophytes and mesophanerophytes (M]M). The 

 megaphanerophytes are trees that are over 30 meters high while the 

 mesophanerophytes are trees from 8 to 30 meters high. Since the 

 buds are freely exposed in both they are grouped together. 



4. Microphanerophytes (M). These are small trees and shrubs 

 from 2 to 8 meters high. 



5. Nanophanerophytes (N). Shrubs that are less than 2 meters 

 high. All trees and shrubs may be spoken of simply as phanero- 

 phytes. 



6. Chamaephytes (Ch). These are plants that have their buds 

 or shoot apices perennating on the surface of the ground or just 

 above it, so that in regions with snow they are protected during the 

 winter and in regions with dry seasons some protection is afforded 

 by plant remains. The buds are thus better protected than in 

 phanerophytes. Plants with runners, cushion plants, etc., belong 

 in this group. 



7. Hemicryptophytes (H). These plants have dormant buds 

 in the upper crust of the soil just below the surface. The aerial 

 parts of these plants are herbaceous and die down at the beginning 

 of the critical season so that they form an additional protection. 

 ]\Iost rosette plants belong here. 



8. Geophytes (G). The geophytes have their dormant parts 

 subterranean. They are plants with bulbs, rhizomes, tubers, etc. 



9. Helophytes and hydrophytes (HH). The heloph^tes are 

 marsh plants with their buds at the surface of the water or in the 

 subjacent soil. The hydrophytes are water plants with perennating 



