THE ESSENTIAL ELEMENTS 417 



the water or salts employed, or dissolved from the walls of the glass vessel 

 containing the culture fluid, may produce a marked effect, especially in 

 fungi, c., although the traces present may be so minute that the tests 

 employed fail to reveal them l . Even when the total amount present in 

 the culture solution is excessively small, it is by no means negligible, 

 for Benecke 2 has shown that the presence of as little as 0-00003 per cent, of 

 potassium distinctly promotes the development of Aspergillus. Similarly it 

 has not been found possible to completely suppress the development of fungi 

 by the removal of all iron, even when the fungal power of collecting any 

 iron present has been utilized by removing the first crop from the culture. 

 Nor has a flowering plant ever been developed in the complete absence of 

 silicon and sodium, a condition which, however, could only be secured by 

 cultivation in a fluid which was not in contact with glass. 



Both seeds and spores always contain a certain amount of the essential 

 elements, and by means of these a bean may be able to develop as far 

 as the formation of flowers when supplied with pure water, and may attain 

 a dry weight two to four times greater than that of the seed 3 . In the 

 absence of iron again, the first two or three leaves of maize or buckwheat 

 seedlings become green at the expense of the iron stored up in the seed, 

 while the subsequent ones remain chlorotic and without chlorophyll. 



In a starved green plant, as well as in a fungus, the iron and potassium 

 may be removed from the older dying organs and transferred to the 

 younger growing parts, so that growth may not immediately cease. 

 Indeed continued development would be possible if, as is unfortunately not 

 the case, the deficient element was necessary only during development of 

 each new organ, and was then entirely available for use elsewhere. 



The effect of the absence of any particular element can only be 

 clearly distinguished by comparing the increase in weight of a plant grown 

 under these conditions with that of a normal one, and it is best to use seeds 

 or spores which contain but little stored nutriment. The entire absence of 

 a non-essential substance is only possible when seeds are used which were 

 borne by plants grown in the absence of the element in question. 



History and Methods. [Nehemiah Grew was perhaps the first to show that 

 calcined plants yield an ash which contains various soluble salts (Anatomy 

 of Plants, 1682, p. 258). Grew also found that different parts contain different 

 amounts of ash, and that hardly any residual ash remains when starch is 

 burnt.] It was some time after the atomic theory had been established that the 



1 On the production of pure water, &c., and the various precautions necessary, cf. the works of 

 Benecke and Molisch. Glass vessels may be employed, which are covered internally with a film of 

 paraffin. 



a Benecke, Jahrb. f. wiss. Bot, 1895, Bd. xxvni, p. 502. 



3 Cf. Boussingault, Agron., Chim. agric , &c., 1860, T. I, p. 64. 

 PFEFFER E 6 



