DESERT VEGETATION OF AMERICA 157 



undertaken the task of trying to make some American desert 

 statistics in the field after this scheme. Yet from complete 

 plant-lists biological spectra can be made but there must neces- 

 sarily be some mistakes as to the growth-forms to which the 

 different species belong. In what follows an attempt will be 

 made to construct biological spectra of the deserts we saw during 

 the I. P. E. in America, but no attempt will be made to make 

 statistics of the frequency of the growth-forms, as this work 

 must be done in the field. 



First it will be appropriate to define the biological types 

 (growth-forms) established by Raunkiaer. 



The Fanerophytes (trees and shrubs) constitute the first 

 type, their dormant buds being attached to branches which 

 project freely into the air. They are in a certain sense the least 

 protected and accordingly are very dominant in countries where 

 the conditions are always favourable (moist tropics). 



The next group is the Chamaephytes, with their dormant 

 buds situated on the surface of the soil or just above it (limit: 

 30 cm.). They include plants with above-ground creeping 

 and persistent shoots, cushion-plants and undershrubs, the lat- 

 ter being conspicuous by the distal or apical parts of the shoots 

 dying away during the unfavourable season. 



Then follow the Hemicryptophytes which have their buds 

 placed in the surface of the soil. 



The Cryptophytes form the fourth group characterized by 

 the dormant buds being subterranean or subaquatic. Aquatic 

 plants have been omitted in this paper, only Geophytes are 

 reckoned with. 



The Therophytes or plants of the favourable season are the 

 best protected, as they live through the unfavourable season 

 as seeds; they are thus annual plants. 



These groups are further subdivided but no use is made of 

 the subdivisions here, as the writer is not well enough acquainted 

 with American plants. 



The procedure in making the biological spectra was this: 

 The plants were listed, the growth-form for each plant was 

 determined (partly in the herbarium of the Botanical Museum 



