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THE POPULAR SCIENCE MONTHLY 



For example, when the roble oak and the enema oak are growing 

 together, and the ground is cultivated beneath them, there is a differ- 

 ence in response of the cultivated plants, which appears not to be 

 directly traceable to the fact that one of the oaks is deciduous and the 

 other is evergreen. Thus, it is known that such cultivated plants, when 

 given water artificially, may thrive beneath the roble oak, while they 

 may dry readily beneath the enema oak, thus indicating that the 

 roble oak does not form a marked superficial root system, even under 

 such conditions. Under such conditions, also, the encina oak absorbs 

 water freely and grows vigorously. Whether, on the other hand, the 



Pig. 4. Quercus Douglasii on an Arid Hill near San Miguel, where the Water 

 Table lies at a Depth of about 75 Feet. The sh.illow placing of the roots, as well 

 as their general character, are shown in the figure. 



converse condition would obtain if agrifolia were grown in the habitat 

 especially characteristic of Jobaia has not been observed. From the 

 nature of the development of the root system of the species, and its 

 plasticity, this might be expected. The characteristic root develop- 

 ment of the blue oak would lead one to suspect, also, that, given 

 abundant soil moisture and adequate depth of soil, the roots might be 

 induced to penetrate deeply. This condition, however, has not been 

 actually observed. 



Ground Water 



The depth to the water table in the valleys is variable, and, in the 

 habitats characteristic of the three species of oaks, unlike. In the 



