Vegetation Groups of the Laboratory Domain. 289 



VEGETATION GROUPS OF THE DESERT LABORATORY 



DOMAIN. 



By J. J. Thornber. 



A list of plants found growing by the writer on the domain 

 of the Desert Laboratory near Tucson, Arizona, has recently been 

 published (Publication No. 113) by the Carnegie Institution 

 of Washington. The list includes 449 species distributed over 

 four well-marked areas, viz.: (i) Tumamoc Hill, the mass of 

 volcanic rock on which the Desert Laboratory is situated; 

 (n) The long slope lying at the foot of the hill and beyond; 

 (in) The flood plain of the Santa Ciuz river; (iv) Santa Cruz 

 river and irrigation ditches. The species of each of the above 

 areas have been grouped under the following vegetation forms: 

 (1) trees; (2) shrubs; (3) woody climbers; (4) dwarf shrubs; (5) 

 half shrubs; (6)perennial herbs; (7) biennial herbs; (8) annual 

 herbs including (a) long-lived annuals; (b) winter annuals; (c) 

 summer annuals. 



The accompanying table presents the various species from 

 the standpoints of habitat and vegetation form. 



Vegetation 

 forms 



Trees 



Shrubs 



Woody-twiners. 

 Dwarf-shrubs . . 

 Half-shrubs. . . . 

 Perennial herbs. 

 Biennial herbs.. 

 Annual herbs: 



(a) Long-lived. . 



(b) Winter an'ls 



(c) Summer an'ls 

 Alga 



Total 



Tumam- 

 oc Hill. 



2 



16 

 2 



13 

 21 

 38 

 1 



38 

 7 



II. 

 Mesa- 

 like 

 moun- 

 tain 

 slopes. 



38 



2 

 10 



4 

 7 

 24 

 1 



9 

 47 

 25 



III. 



Santa 

 Cruz 

 flood- 

 plain. 



11 



10 

 3 



3 

 33 

 1 



28 

 13 

 12 



129 



116 



IV. 

 Santa 

 Cruz 

 River 

 and irri- 

 gation 

 ditches. 



14 



Intro- 

 duced 

 species. 



20 

 24 



52 



Total. 



15 

 39 

 5 



17 



32 

 108 

 3 



57 

 124 

 44 

 7 



449 



