8 CONCEPT AND HISTORY. 



Hilgard, 1906.— In summarizing his soil studies of more than 50 years, Hil- 

 gard formulated more fully and definitely his ideas of the indicator value of 

 native vegetation. This account makes it clear that to Hilgard must be given 

 the great credit of being the first to adequately realize the significance of indi- 

 cators and to urge their inclusion in a basic agricultural method. 



"The importance of the natural relations of each soil to vegetation is obvi- 

 ous, both from the theoretical and from the practical viewpoint. From the 

 former, it is clear that the native vegetation represents, within the climatic 

 limits of the regional flora, the result of a secular process of adaptation of 

 plants to climates and soils, by natural selection and the survival of the fittest. 

 The natural floras and silvas are thus the expression of secular, or rather 

 millenial experience, which if rightly interpreted must convey to the cultivator 

 of the soil the same information that otherwise he must acquire by long and 

 costly personal experience. 



"The general correctness of this axiom is almost self-evident; it is explicitly 

 recognized in the universal practice of settlers in new regions of selecting lands 

 in accordance with the forest growth thereon ; it is even legally recognized by 

 the valuation of lands upon the same basis for purposes of assessment, as is 

 practiced in a number of States. 



"The accuracy with which experienced farmers judge of the quality of tim- 

 bered lands by their forest growth has justly excited the wonder and envy of 

 agricultural investigators, whose researches, based upon incomplete theoretical 

 assumptions, failed to convey to them any such practical insight. It was 

 doubtless this state of the case that led a distinguished writer on agriculture 

 to remark, nearly half a century ago, that he 'would rather trust an old farmer 

 for his judgment of land than the best chemist alive.' 



"It is certainly true that mere physico-chemical analyses, unassisted by 

 other data, will frequently lead to a wholly erroneous estimate of a soil's 

 agricultural value, when applied to cultivated lands. But the matter assumes 

 a very different aspect when, with the natural vegetation and the correspond- 

 ing cultural experience as guides, we seek for the factors upon which the 

 observed natural selection of plants depends, by the physical and chemical 

 examination of the respective soils. It is further obvious that these factors 

 being once known, we shall be justified in applying them to those cases in 

 which the guiding mark of vegetation is absent, as the result of causes that 

 have not materially altered the natural condition of the soil. (p. xix.) 



"It was from this standpoint that the writer originally undertook, in 1857, 

 the detailed study of the physical and chemical composition of soils. It 

 seemed to him ' incredible ' that the well-defined and practically so important 

 distinctions based on natural vegetation, everywhere recognized and contin- 

 ually acted upon by farmers and settlers, should not be traceable to definite 

 physical and chemical differences in the respective lands, by competent, 

 comprehensively trained scientific observers, whose field of vision should be 

 broad enough to embrace concurrently the several points of view — geological, 

 physical, chemical, and botanical — that must be conjointly considered in 

 forming one's judgment of land. Such trained observers should not merely do 

 as well as the 'untutored farmer,' but a great deal better." (p. 315.) 



This attitude toward plants and vegetation as indicators prevails through- 

 out the book, and the subject is treated in considerable detail for the first time 

 in Chapters XXIV to XXVI. These deal respectively with the recognition of 

 the character of soils from their native vegetation, in Mississippi, and in the 

 United States and Europe generally, and with the vegetation of saline and 



