ASH. 11 99 



Although further investigations may not confirm the view that carbonate of 

 lime is directly poisonous to higher plants, still they may establish that this sub- 

 stance has an indirect effect such as may be deduced from the experiments of FLICHE 

 and GRANDE AU (1873). These investigators analysed the ash of trees which had 

 been grown in normal soil and compared it with that of other specimens which 

 had passed a miserable existence in a soil which was rich in lime. The result of this 

 comparison was to show that the ash of those grown in a siliceous soil contained 

 40-45 per cent, of lime, while in those from a lime soil, the percentage rose to 56- 

 75 ; at the same time the absorption of potassium was much reduced (from 16-22 

 per cent, down to 4-6 per cent.). It is conceivable that the diminution in the 

 absorption of potassium is due to the fact that the calcium carbonate rapidly 

 neutralizes the acid excretions of the root, and so interferes with its disintegrating 

 action on rock material naturally difficult of solution. In addition to the diminu- 

 tion in potassium there is a scarcity also of magnesium and iron in plants grown 

 in lime soils. SCHIMPER (1898, no) attributes the feeble development of 

 siliciferous plants on lime soils to the deficiency in iron. In support of this 

 view one may cite the fact that calciphobous plants become chlorotic on 

 lime soils (Roux, 1900), and that this chlorosis (according to a verbal state- 

 ment of Professor STAHL) can be set right by spraying with a solution containing 

 iron. [BENECKE has obtained marked chlorosis in presence of iron when the 

 water-culture gave an alkaline reaction (Bot. Ztg. 1904, 62, II, p. 124).] 



A complete explanation of the aversion of many plants to lime is not at 

 present available ; we must be content with the suppositions advanced above. 

 Nor are we better off in regard to our knowledge of the reasons for the fondness 

 for lime exhibited by other plants. The view once held that these plants avoid 

 contact with silicic acid need not be considered. That they can endure the 

 presence of more lime than others can is obvious, but it is not so apparent what 

 use they make of it. THURMANN has performed a useful service in demonstrating 

 the physical differences between lime and sandy soils, especially the deficiency 

 in water in the former and its abundance in the latter, and has suggested this 

 as determining questions of plant distribution. According to THURMANN, 

 ' calciphilous ' plants are xerophytes, ' calciphobous ' forms are hygrophytes, 

 and it is quite true that we do meet with plants in the most varied regions 

 which usually occur on chalk or, exceptionally, on primitive rock under very 

 dry conditions. THURMANN, for example, has emphasized the fact that quite a 

 series of calciphobous plants in Southern France also occur on primitive rock. 

 This, however, must depend not only on the amount of water present, but on the 

 sum- total of the physical characters of the soil, and amongst these the conditions 

 of temperature at all events must be especially taken into account. These con- 

 ditions have been specially investigated in recent times by WOLLNY (1898); 

 It has been shown that a quartz soil changes most rapidly with alterations 

 in the temperature of the air, then more slowly clay, lime, and magnesia soils 

 respectively, and, finally, humus soils change most slowly of all. Chalk soils 

 moderate the extreme temperatures of the air, being cooler in summer and 

 warmer in winter than sandy soils. 



NAGELI (1865) has shown that it is as yet impossible to explain completely 

 the distribution of plants by reference only to the chemical and physical characters 

 of the soil ; this he has proved in a classical treatise in which he draws attention 

 to two new factors, hitherto entirely disregarded, which take part in determining 

 the distribution of plants on the earth's surface. He starts from the fact, already 

 referred to above, that a plant may be local in distribution in one district and 

 indifferent in another, or that one and the same species may be calciphobous ia 

 one region and calciphilous in another. NAGELI' s well-known researches were per- 

 formed on Achillea atrata and Achillea moschata, and we will take these also as our 

 illustrations. NAGELI found both species extremely restricted in distribution in 



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