236 W. A. CANNON 



extent is not as yet known. A similar root type has been seen in 

 the buckeye, Aesculus calif ornicus, and in other forms. It may 

 be concluded, therefore, that in regions of a fair but periodic, 

 rainfall, as in California, the root-systems of the leading types of 

 trees exhibit a two-fold habit — they may penetrate fairly deeply 

 and at the same tune they may have a large development near the 

 surface of the ground It is probable that the condition of youth 

 is characterized by deeply penetrating main roots, but that as 

 the tree matures the superficial roots are the ones mainly formed. 

 The end result is that the mature plants are adjusted to absorb 

 the most of their water from the superficial soils, while at the 

 same time a certain amount, which may be sufficient to tide them 

 over during the droughts, is taken up from greater depths. 



Without following the subject farther it will be quite clear, I 

 suspect, that the fog relations of the redwood and the behavior 

 of the roots of the different species of oaks, all point to this — ^that 

 the moisture relation is of the first importance. We may say, 

 therefore, that we needs must pay first attention to the moisture 

 relation in seeking a key to explain many of the leading features 

 of the California flora. 



The leading idea in this paper can be characterized in a few 

 sentences. It has been shown that the climate of California is a 

 very diverse one and that its diversity is directly associated with 

 the state's great physiographic complexity. Thus, the environ- 

 ment is highly specialized. In association, or possibly conformity, 

 with such specialization the flora is likewise extremely diverse 

 and may be highly specialized, as is exhibited in a number of 

 ways. One of these is shown by the similar stamp put on the 

 flora of areas over which some one environmental character is 

 especially prominent, as, for example, the dwarf forest, or chap- 

 arral, which is the leading plant type in the moderately arid 

 regions, especially of the south. Another floral specialization is 

 shown in the limited distribution of many species some of which 

 are restricted to a single locality. And, in yet another manner the 

 response is seen in the individual adjustment to the impinging 

 environment. This occurs in numberless ways, of which in- 



