160 OVE PAULSEN 



not characterised by them as is Akron. Here, in Tucson, Thero- 

 phytes are very prominent, and the Fanerophytes are rather 

 numerous. 



4. Salton Sink is like Tucson, the only difference being that 

 Fanerophytes have increased at the cost of Hemicryptophytes 

 being still under the percentage of the normal spectrum. Death 

 Valley shows the same features. 



Summing up, we find three distinctly different types of plant- 

 communities namely : 



Hemicryptophytic : The Colorado plains. 



Chamaephytic : The Utah desert. 



Therophytic : The Tucson, Salton and Death Valley deserts. 



The yearly precipitation of Akron, Tooele and Tucson is 

 respectively 47, 40, and 27 cm., 1 of Salton hardly over 20 cm. 

 So we find a coincidence of drier climate with development of 

 other growth-forms: Hemicryptophytes give way to Chamae- 

 phytes and these to Therophytes and partly Fanerophytes. 



In the old world we have at least partly a parallel transition: 

 in Southern Russia Hemicryptophytes dominate (the govern- 

 ment of Jekaterinoslaw has 55%), and in Transcaspia Thero- 

 phytes preponderate (41%); as to Fanerophytes the percentage 

 of the two regions is respectively 5 and 11%. Thus also here 

 there is a parallelism. The interjacent Chamaephyte region 

 has not been numerically demonstrated in the old world, yet we 

 know that in the countries between Southern Russia and Trans- 

 caspia proper waste regions are covered with a vegetation of 

 Artemisias and similar plants. So we may be justified in believ- 

 ing that the Chamaephyte region is there. 



Finally it should be emphasized that the material upon which 

 my conclusions are based is not complete and that if perfect 

 biological spectra could be made they would without doubt 

 give a more vivid and detailed picture of the relations between 

 plains and different deserts in America. Yet I hope that there 

 are no fatal errors in the preceding remarks. 



1 Quoted from Kearney, Briggs, Shantz, McLane and Piemeisel and from 

 Briggs and Belz. 



