106 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. 
the four areas, as against 68 per cent of the shrubs and g1 per cent of 
the dwarf shrubs and half-shrubs for areas I and II. 
The plants which are characteristic of alkaline situations are ro in 
number, all inhabitants of area III. The most important are members 
of the Chenopodiacee, 3 being shrubs, 2 half-shrubs, and 1 an annual herb. 
Four other families of plants are represented with one species each. 
The exotic plants that have become established in a new country are 
always an interesting group. Especially is this true in a region like our 
own, where the various factors are so sharply defined as to leave little 
doubt concerning the particular character or characters of a plant which 
makes for its success. Of the introduced species taken as a whole, 47 
per cent deport themselves as winter annuals. It is a fact worthy of note 
that with few exceptions these exotic winter annuals are natives of the 
Mediterranean region of the Old World. Our climatic conditions, which 
are quite similar to those of southern Europe and especially northern 
Africa, appear to be so entirely adapted to their manner of growth that 
many of them have little difficulty in securing a foothold here. Several 
of these species, among which are Evodium cicutarium and Hordeum mu- 
rmum, are becoming common plants upon the mesas; especially the former, 
which in many localities in Arizona at this time is more abundant than 
any other species during its period of growth.! Another species worthy 
of mention here is Matthiola bicornis. Seven years ago this plant, appar- 
ently an escape from nearby flower-beds, was represented by a few scat- 
tered individuals on the mesas near the University. At the present time 
it occurs in considerable abundance in this vicinity; besides, it has been 
observed growing on the flood-plain and even across the river on the mesa- 
like mountain slopes. 
The composition of the flora of the Desert Laboratory domain and 
adjacent areas as concerns the more important plant families represented, 
together with the number of species for each, in addition to which there 
are 38 other families with 1 to 3 species each, is as follows: 
Grannnes.. 2 o. 70 Polygonacee....... 12 Plantaginacee..... 5 
Conipositieqs = cece 65 Cichoriates. Geen. II Polypodiaceze...... 5 
Solanaceae Be 16 Nyctaginacez...... 9 Portulacacess © 2a.) 5 
Crititeras 6 eee 16 Ceesalpinacee...... 8 Acanthaces 02) 4 
Euphorbiaceze...... 16 Polemoniacee...... 7 Asclepidacez....... 4 
Boraginacee....... 15 Hydrophyllacee.... 6 Convolvulacee..... 4 
Malvaces..... 0 ee ‘6 PAE ae et 6 Liliacese fa, o2 eee 4 
Chenopodiacez.... . I4 Mimosacee........ 6 Ranunculacee..... 4 
CACtACE iy Werte 13 Onartacée saa... 6 Scrophulariacee.... 4 
Papilionacee....... 12 Amaranthacee..... 5 Zygophyllacee..... 4 

1Thornber, J. J. Alfilaria (Erodium cicutarvum) as a Forage Plant in Arizona. Bull. 
52, Ariz. Exp. Sta., May, 1905. 
