112 



The Plant World. 



fall. At Palm Springs, California, where the annual rainfall is 

 only three and one-half inches, an olive plantation of twenty 

 acres has been found which was planted in 1891, and in which 

 the greater number of the original trees are now in vigorous 

 condition, six years after the failure of the irrigation supply. 

 These trees have developed the same minutely divided type of 

 roots noted at Casa Grande, occupying the first foot of soil very 

 completely for an area often eight or nine times that of the spread 

 of the tops. Under these circumstances, if the trees are planted 

 too closely, such competition for soil moisture must result as to 

 interfere with growth that would take place were they planted 

 farther apart. The results of this unintentional experiment, 

 instituted years ago and now interpreted by a scientific observer, 

 furnish important evidence regarding the competition of desert 

 plants, which is plainly a far more prominent factor, as regards 

 their biological relations, than has hitherto been held, and one 

 which is of prime importance in horticultural undertakings in 

 the semi-arid regions of the Southwest. 



The investigations conducted in the Physical Laboratory 

 include, among various other undertakings, a comprehensive 

 study of environmental factors at different stations and the re- 

 lation of these factors to the growth and yield of the principal 

 crop plants. Such determinations are a necessity in the proper 

 interpretation of cultivation and rotation experiments, and the 

 observation of both normal and abnormal conditions now in 

 progress serves to show the actual merits of the different methods 

 employed in conserving the moisture and maintaining the fer- 

 tility of the soil. The great practical importance of this work, 

 it is needless to say, in no wise detracts from its value as a con- 

 tribution to pure science, and the same obvious fact is continually 

 impressed on one who proceeds through the report and notes 

 the extended studies which have been made of the relations of 

 both cultivated and native plants to their environment, the power 

 of resistance of certain varieties to drought, cold and other in- 

 jurious influences, acclimatization and the adaptation of prom- 

 ising plants to special conditions, the transmission of valuable 

 characters, in short, a body of physiological, pathological and 

 other investigations, that would be appalling but for the systematic 

 division of labor on the part of the experienced investigators 



