Vol.1] Hall. — Boimiical Surrey of San Jacinto Mountain. 17 



We now know that these formations are bronght about by a 

 combination of conditions to which each of the formation elements 

 is adapted. Some would use the term in this ecological sense, and 

 Schimper, in his great work on plant geography,* has recently 

 defined it as an assemblage of plants determined by the qualities 

 of the soil. But a formation may be determined by other condi- 

 tions, such, for example, as those controlling the dissemination 

 of seeds. Moreover in making a botanical survey of a region 

 the plant formations first engage our attention and the inciuiry 

 as to the causes which have produced these formations naturally 

 comes up later, and not until their nature is understood. It is 

 therefore necessar}^ to have some term by which to designate 

 them, without any reference to their origin, and this is found in 

 the term formation, used in its original meaning. 



Some have limited the meaning of this term by using it to 

 designate an assemblage of plants marked by a dominant species, 

 instead of by a dominant physiognomic t.ype. The value of this 

 is not evident, and the practice of certain recent phytogeog- 

 raphers of dividing and sul)dividing each formation until scarcely 

 more than a single species is left in each division is not followed 

 in this paper. Wherever it has seemed advisable to discuss the 

 individual species of a formation it has been done in the main 

 part of the report, where they will be found arranged according 

 to a well known system. The only departure from this rule is 

 in the case of the Coniferae, the species of which will for evident 

 reasons be taken up in this chapter. 



THE CHAPARRAL FORMATIONS. 



On San Jacinto Mountain are found two distinct chaparral 

 belts, the one belonging to the low, foot-hill region, the other to 

 the higher slopes. These are distinct not only in composition 

 but also in position, the species found growing in the one never 

 occuring in the other, and for this reason it has seemed best to 

 consider them as separate formations and of these the one of the 

 foot-hills, which is indicated on the map of life zones bj' the 

 purple coloring, will be first taken up. 



*A. F. W. Schimper, Pflanzengeo^raphie 175 (1898). See also Ch. Flahault 

 on A Project for Phytogeographic Nomenclature, Bull. Torr. Club xxviii. 391 

 (1901), (translation). 



