THE VOICE OF THE DESERT 



128 



long way from being a full answer. Some don't live where 

 they very well could for the same reason that, for centu- 

 ries, Europeans did not live in America — they had just 

 never got there. Others don't because there are many 

 things besides temperature to which some are absurdly 

 sensitive. 



Some of the subtler demands are only now beginning to 

 be understood. For instance: some southern plants won't 

 bloom and therefore can't reproduce themselves even in 

 northern greenhouses, because the summer days are too 

 long and give them too many hours of light; other plants 

 will not flower except in isolated areas even within their 

 geographical range, because they demand infinitesimal 

 traces of certain chemical elements not everywhere pres- 

 ent. That is probably why, a few miles south of Tucson 

 and not far from the Mexican border, one will see in 

 spring certain hillsides covered with yellow poppies, while 

 another apparently identical hillside a few hundred yards 

 away has none. As has only recently been demonstrated 

 these poppies like a trace of copper, which happens to be 

 present in some places and not in others. 



Dates from the Near East will grow wonderfully here 

 but in many places only if they are irrigated more than in 

 their native desert habitat, because there is often less ^sub- 

 surface water in Arizona than in some parts of even the 

 Sahara. And as we have already remarked, most of the 

 palms which tourists admire as exotics along the Riviera 

 are actually imports from California favored in Europe 

 because they stand lower temperatures than most African 

 palms like. By way of compensation, the tamarisks, which 

 took firm hold here in the Southwest when planted by the 



