FACTOR INDICATORS. 85 



One by one the " calciphile " and "calciphobe" species have been found or 

 grown in the opposite conditions, until practically no obligate species remain. 

 The present situation is well-expressed by Wanning (1S09 : 58) : 



" Recently it has been definitely established that the amount of lime in itself, 

 in so far as it does not operate physically, can not be the cause of differences in 

 the flora, for not only can calcicolous plants be cultivated in soil that is poor 

 in lime, but silicolous plants, and even bog-mosses, which are regarded as pre- 

 eminently calciphobous, can grow vigorously in pure Ume-water if the aqueous 

 solution be otherwise poor in dissolved salts. It has been overlooked that 

 nearly all lime soils are rich in soluble mineral substances, and this wealth 

 excludes plants belonging to poorer soils ; beyond this the important physical 

 characters of calcareous soil, compared with granite soil, come into play." 



The century-old controversy over the significance of lime has been as 

 unscientific as it has been useless. No ecologist questions the influence of 

 both the chemical and physical properties of the soil, though there can still be 

 much opportunity for disagreement as to their respective importance, where 

 observation is the method relied upon. The general employment of quanti- 

 tative methods and experiments in the fields would long ago have assigned to 

 lime its proper position. Naegeli (1865) was perhaps the first to point out that 

 the response to lime was largely a matter of competition, and the validity of 

 this explanation has been greatly increased by cultures showing the facultative 

 nature of "calciphile" and "calciphobe" plants. His conclusions were based 

 upon observational studies, however, and, like all such work, can only suggest 

 working hypotheses for critical field experiment. The following statement 

 (Clements, 1913 : 76) seems still an adequate summing-up of the lime problem: 



"To one skeptical as to the influence of lime, the results of the Excursion 

 were most interesting. One could not fail to be impressed with the abundant 

 evidences of the distributional significance of lime, while he was struck by the 

 fact that scarcely a single 'calciphilous' or 'calciphobous' plant could prove a 

 clear title to the term, physiologically. It is useless to add a single line to the 

 Uterary solution of this hoary problem, but the British experience serves to 

 emphasize the conviction that nothing but physiological and competition 

 studies in the field can hope to lead to a final solution." 



In the western United States lime has nowhere been found to be a direct 

 factor of importance. Neither observation nor experiment has disclosed any 

 definite correlation with it, and hence no plants have been found which can be 

 regarded as hme indicators. The plants of wet soils which have been con- 

 sidered to indicate the absence of lime are dealt with in the next section. 



Aeration indicators. ^The effects of wet and acid soils upon plant behavior 

 have long constituted a puzzling problem. The leading r61e in such habitats 

 as marshes and bogs has been assigned to various factors, such as acids, bog 

 toxins, toxic exudates, the absence of lime, and the lack of oxygen. Probably 

 all of these are more or less concerned in the problem, with the exception of 

 the supposed exudates, but the view held here is that the lack of oxygen is the 

 cause, and the other conditions, consequences, or concomitants (Clements, 

 1916 : 90). The presence of acids and bog toxins is regarded as the direct 

 result of the activity of the roots and bog flora under deficient aeration (cf. 

 Stoklasa and Ernest, 1909 : 55; Livingston, 1918 : 95). The absence of lime 

 is apparently a concomitant of acid production, since the addition of lime to an 



