292 



The Plant World. 



tant are members of the Chenopodiaceae, 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 charac- 

 ter or characteis of a plant which makes for its success. Of the 

 introduced species taken as a whole, 47 pel cent deport themselves 

 as winter annuals. It is a fact worthy of note that with few ex- 

 ceptions these exotic winter annuals are natives of the Mediter- 

 ranean legion of the Old World. Our climatic conditions, which 

 are quite similar to those of southern Europe and especially north- 

 ern 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 arc 

 Erodium cicutarium and Hordeum murinum, are becoming com- 

 mon 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. * Anothei species 

 worthv of mention here is Matthiola bicornis. Seven years ago 

 this plant, apparently an escape from nearby flower-beds, 

 was represented by a few scattered individuals on the mesas 

 near the University. At the present time it occurs in consider- 

 able 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: 



Gramineae 70 Polvgonaceae 12 Plantaginaceae 5 



Composite 65 Cichoriaceae 11 Polypodiaceae 5 



Solanacese 16 N yctaginaceae 9 Portulacaceae . . . . . . 5 



Cruciferae 16 Caesalpinaceae 8 Acanthaeeae 4 



Euphorbiaceae 16 Polemoniaceae 7 Asclepidaceas 4 



Boraginaceae 15 Hydrophyllaceae. . . . 6 Convolvulaceae 4 



Malvaceae 15 Labiataae 6 Liliaceae 4 



*Thornber, J. J. Alfilaria (Erodium cicutarium) as a Forage Plant in Arizona. Bull 

 J2. Ariz. Exp. Sta., May, 1905. 



