550 



SCIENCE 



[N. S. Vol. LI. No. 1326 



soil unknown This sawdust would represent 

 a mixture of samples from numerous trees 

 and possibly represent several species grown 

 on ordinary forest soils. 



Prom these analyses several interesting con- 

 clusions are to be drawn. The dune plants 

 have obtained and concentrated in their 

 tissues, the same mineral constituents com- 

 monly found in plants growing on good soils, 

 and these have been accumulated in approxi- 

 mately the same relative proportions. It is 

 natural to suppose that the concentrations of 

 the various substances in the soil would have 

 some influence on the composition of the ash. 

 If a soil contain a relative^ large amount 

 of potassium or phosphorus, or calcium or 

 silicon, one might expect that these elements 

 would be contained in the plant ash in rela- 

 tively large proportion. While this influence 

 of total quantity present in the soil is of some 

 effect, it is not determinative. The plant 

 takes what it needs. Contrast Prunus with 

 Artemisia, Quercus or the three grasses or 

 the scomring rush and note the astonishingly 

 low silica content of Prunus ash compared to 

 any of the others and the relatively high cal- 

 cium. It is astonishing indeed to find a 

 negligible quantity of silica and an extremely 

 large proportion of calcium in the ash of a 

 plant grown on such a highly silicious soil. 

 Consider those elements derived from the 

 soil which are assumed to fim.ction in the 

 essential metabolism of the plant, iron, man- 

 ganese, calcimn, magnesium, potassium, phos- 

 phorus, sulphur. From most inadequate and 

 insufficient sources the dune plants have ob- 

 tained their requirements of these necessary 

 elements. On such a soil as beach sand, the 

 ordinary plants of agriculture woiold wilt and 

 starve. It would probably not be possible to 

 successfully grow any sort of plant which in 

 addition to maintaining itself normally, 

 stores up abundantly large quantities of or- 

 ganic compounds suitable for human food in 

 roots, leaves, fruits or grains. Plants of this 

 sort would probably not reach maturity or 

 grow at all. Certainly they would not de- 

 velop into a food-producing crop, but the 

 characteristic dune plants are at least suffi- 



cient unto themselves, carry through their 

 life cycle successfully and win from a most 

 refractory soil their necessary mineral sus- 

 tenance. Prunus refuses silicon and gathers 

 in large supplies of calcium whereas the 

 grasses and the scouring rush store up large 

 quantities of the former and are satisfied with 

 one fourth to one third as much calcium as 

 Prunus requires. 



Those other elements, aluminium, silicon, 

 sodium and chlorine, consistently present in 

 plants, but apparently not essential to growth 

 (as determined by pot and water cultures) 

 are yet present in the ash of dune plants, 

 although, with the exception of silica, in 

 small proportion. Must we conclude that 

 these elements although not essential to 

 growth, are nevertheless not harmful, and 

 that they are absorbed by a selective apparatus 

 which while highly efficient is not absolute in 

 its action, since the physiological require- 

 ments of the plant are satisfied short of 

 positive rejection of harmless non-essentials? 

 Or, on the other hand, are some or all of 

 these elements, while not necessary for the 

 normal metabolism of the plant, at least 

 desirable in some unknown way in connection 

 with osmotic pressures? 



The older chemists puzzled much over the 

 meaning of plant ash composition and not 

 without reason. However regrettable the fact 

 is, we are forced to admit that to-day we know 

 little more in regard to the fundamental re- 

 quirements of plants as regards mineral sub- 

 stances and the ability to obtain them from 

 various soils and under various conditions 

 than they did. In Liebig^ are some hundreds 

 of analyses in the old chemical notation vm- 

 classified save as to species and with the com- 

 ponents in every conceivable proportion. The 

 names of the analysts are appended but this 

 throws little light on the subject as some of 

 them are known to fame, others all but lost in 

 oblivion, and as the methods of analysis used 

 by the various investigators are not given, 

 the degree of accuracy attained in the various 

 cases remains imknown. Undoubtedly the 



7 ' ' Die Chemie in ihxer Anwendimg auf Agricul- 

 tur und Physiologie. " 



