16 The Pi.ant World, 



of plants native to arid or semi-desert regions similar to our own, 

 as for example the plants from the Mediterranean region, 

 are almost certain to flourish from the very start with us. This 

 applies not alone to the numerous weeds that have already 

 found their way here without encouragement, but also to vari- 

 ous economic species introduced from time to time by man. 



So clear-cut are the climatic elements over parts of the 

 Southwest, particularlythose influencing the growth of plants, that 

 modifying by even a few degrees the maximum summer or the 

 minimum winter temperatures, or neutralizing in a small measure 

 the aridness of the fore-summers makes possible the growth of 

 a much large number of species than now obtains. On 

 a small scale this is seen from growing plants under lattice, a 

 practice which is gaining rapidly in parts of the Southwest, and 

 which promises to play an important part in our future horti- 

 cultural operations. In this manner the conditions of heat, 

 light, cold, and aridity are mollified to greater or lesser extents. 

 It is not the average run of climatic factors, however, such as 

 may be noted by a hasty examination of weather records, but 

 rather the extremes of these, that must be taken into account 

 in the introduction of new plant varieties in a locality, and when 

 these are permanently changed by any means whatever, as by 

 lattice construction, the way is opened for the growing of an ad- 

 tional list of somewhat less resistant plants. The behavior of 

 plants when grown at different altitudes under similar cultural 

 conditions throws additional light on this matter of varying or 

 modifying the important factors of plant growth, though here 

 the subject is rendered somewhat complex by the addition of 

 other factors, the effects of which cannot be foretold. 



In this paper it is desired more especially to call attention 

 to some plants that ordinarily do not thrive under our conditions. 

 If it were possible to make a careful study of all the causes, 

 direct or indirect, contributing to failure among introduced 

 species, the results would be not only interesting scientifically, 

 but of inestimable value to the planter and horticulturist. Such 

 a study would enable one to predict more accurately the probablje 

 success of plants when transplanted to other countries, and to 

 guard against the introduction of species that later might be- 

 come dangerous weeds. In short, it would tend to put the inter- 

 esting work of plant introduction on a scientific basis. Besides, 



