Acclimatization in Arizona, 21 



Such hardy weeds as dooryard plantain and dandelion, ever 

 present in lawns and meadows in the central states, are rarelv 

 seen growing in southern Arizona, and then only in the shade of 

 larger plants. These species have been introduced repeatedlv 

 in seeds, as careful examination has shown, but at best they die 

 out in May or June before coming to maturity. For the same 

 reason neither common mullein {Verbascum thapsus), nor moth 

 mullein {Verbascum blattaria), both biennial species from the 

 Old World, grow at our lower altitudes in exposed situations, 

 although both are commonly met with at elevations of 6,000 

 feet and above. 



As concerns the part played by occasional severe freezes in 

 our warmer sections in limiting the number of successful growing 

 species of the introduced flora, only plants from extra-tropical 

 countries need be considered, those from regions farther north 

 being entirely hardy, while tropical plants are, of course, out of 

 the question. There are a considerable number of extra-tropical 

 plants growing in southern Arizona which often endure without 

 njury several mild winters in succession only to be killed later 

 by one much colder than the average, as for example the winter 

 of 1909-1910. Among such plants may be mentioned guava 

 {Psidium guajava), kei apple (Aberia caffra), St. John's bread 

 (Ceratonia siliqua), flame tree (Sterculia acerifolia), Lagunaria 

 Paiiersoni, Pittosporum undulatum, Casuarina equisetijolia, 

 Duranta Pluniieri, Solanum Wendlandii, Tecoma capensis, Tecoma 

 McKennii, and Bougainvillaea spectabilis, in addition to many 

 palms, bamboos, acacias, and eucalypts. Since none of these 

 can tolerate the severest winter weather in southern Arizona, 

 they are excluded from growing elsewhere in the Territorv, except 

 under glass. Curiously enough, with good cultivation, most of 

 these resist well our maximum summer temperatures and 

 but for injury from frosts would prove to be valuable plants 

 in our country. 



To summarize briefly, regarding climatic conditions, the 

 ordinary introduced perennial herbs so much grown in the older 

 settled States have not shown pronounced resistance to the ex- 

 treme heat of our lower altitudes, asparagus being a notable ex- 

 ception; although they commonly thrive at the higher eleva- 

 tions. Many of these are indigenous to countries having cooler 

 growing summers than our own. On the other hand species 



