LIFE FORMS AND SYNECOLOGICAL UNITS 



295 



IX. PHANEROPHYTES (aerial plants) : especially trees and shrubs, bearing their 

 renewal buds upon upright shoots at least 25 to 30 cm. high and therefore more 

 exposed to unfavorable weather conditions than any of the previously mentioned 

 life forms. Their center of distribution lies in the tropics and subtropics. The 

 more northern phanerophytes are characterized by special bud protection, or 

 they make use of the protection of snow by means of low growth. Their resistance 

 to cold is to a large extent due to properties of their protoplasm. 



Fig. 151. 



-A cactoid euphorbia in the Euphorbia rt .^niijcra- Acacia tj.^.ujua scrub at the 

 foot of the Great Atlas, Morocco, 800 m. {Photo by Maire.) 



Among the numerous forms of phanerophytes Raunkiaer (1905) stresses 13 

 main groups, based upon height of plant, duration of foliage, and bud protection. 

 To these are added the succulents and herbaceous epiphytes. For greater sim- 

 pUcity the 13 groups are reduced to the following 5: 



1. Nanophauerophyta (shrubs): renewal buds about 0.25 to 2 m. aboveground; 

 a most varied group with many subdivisions. Important structures that 

 may be used as the bases of further classification arc: foliage, evergreen or 

 deciduous; leaf structure, sclerophyll, needle leaf or rolled leaf; leaf size, 



