12 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



point I intend only to establish the location of the center. The 

 environmental phases of the problem will be considered later. 



LOCATION OF GREATEST DIFFERENTIATION OF TYPE. 



Our first problem under this head is to discover which part of the 

 general region inhabited by the type is richest in species of that type. 

 As a corollary to this, the relative number of endemics in the different 

 areas may be compared. The former is easily done by plotting the 

 ranges of all the species concerned upon a single map and indicating 

 by density of shading the numbers of overlapping ranges. The 

 results are shown in plate 1, the large map in detail for the State of 

 California, the small one in more generalized form for the whole 

 region covered. Some practical difficulty was encountered in super- 

 posing the ranges of so large a number of species. The problem 

 was solved by cutting the ranges from thin cardboard, gluing them 

 together in their proper positions, outlining the total extent indicated, 

 cutting away all portions where five thicknesses of cardboard or less 

 occurred, outlining the remainder, and repeating the process. It is 

 scarcely necessary to state that the map must be interpreted broadly 

 and that details must be disregarded, since in only a few cases has it 

 been possible to draw the ranges with an approach to exactness. 

 The species considered are in general those of lists I and II (see 

 Appendix), the deciduous ones being excluded. A few of the broad- 

 sclerophylls were omitted because of lack of satisfactory knowledge 

 of their ranges. The total number of species considered is 71. 



From the small map we see that, broadly speaking, the type has 

 its stronghold in California and Lower California. A few species 

 extend northward beyond the State line; about 21 into Oregon, many 

 of them a short distance only; 11 into Washington, and 8 into British 

 Columbia. None occurs north of California which does not enter 

 that State, unless we admit Howell's species of Ardostaphylos to 

 consideration. The complete list of those ranging northward beyond 

 California is as follows^ : 



Myrica californica.** Ceanothus cuneatus. Arbutus menziesii.** 



Castanopsis chiysophylla.* sanguineui^.** Arctostaphyloa manzanita. 



sempervirens. thyrsiflorua.* nevadensis.* 



Quercua chryaolepis. velutinus.** patula. 



sadleriana. Garrya elliptica. tomentosa.** 



Pasania densiflora. fremontii. Gaultheria shallon.** 



Umbellularia californica. Rhododendron calif ornicum.** Vaccinium ovatum.** 



Six species extend discontinuously eastward beyond the boundaries 

 of California: 



Cercocarpus ledifoliua. Ceanothus velutinus. 



Rhamnus californica. Arctostaphylos patula. 



crocea. pungens. 



■ Unatarred apecies extend into Oregon only; those with a single star (*) into Washington, 

 and double-starred (**) species into British Columbia. 



