THE NON-ESSENTIAL ASH CONSTITUENTS 437 



growing upon the soil where zinc was most abundant, and this was probably due 

 to the stimulatory action which small doses of poisonous substances may exert 

 upon growth (Sect. 73). 



The other metals of the zinc group, magnesium, beryllium, and cadmium, 

 have been dealt with in the preceding section, where an account is also given of 

 the non-essential alkaline metals and alkaline earths. 



Aluminium, though universally distributed, is present only in small amount in 

 most plants, except in Lycopodium Chamaecyparissus and L. alpinum, where it 

 forms 22 to 27 per cent, of the ash. It is also present in abundance in Chlorangium 

 Jusuffii ', whereas according to Church in Lycopodium phlegmaria, Selaginella, &c. 

 mere traces are present. It is uncertain whether the alumina is present in Lyco- 

 podium in the form of a tartrate as is stated by Arosenius. 



Manganese, though usually much less abundant in the soil than aluminium, 

 seems to accumulate in plants to a more marked extent, and small amounts seem 

 always to be present. The ash of Trapa natans may contain 7-8 to 14-7 per cent, 

 of red oxide of manganese, and a marked accumulation has been observed to 

 occur in many Phanerogams and Cryptogams 2 . The accumulation probably 

 proceeds in a similar manner to that by which an excess of iron may be 

 absorbed. Manganese is also present in the incrustation of iron-oxide formed 

 on or in certain bacteria. 



Cobalt and Nickel have been detected by Forchhammer in oak wood. Nickel 

 seems to be more poisonous than cobalt, and the stimulatory action of both metals 

 has already been mentioned. 



Copper is frequently present in minute quantities, and the ash of plants grown 

 in soil rich in this metal may contain i per cent. The copper accumulates mainly 

 in the older organs, and since it is extremely poisonous it can only be absorbed in 

 minute traces at a time. Even the extremely poisonous Mercury was detected by 

 Gorup-Besanez in plants grown on soil containing mercuric oxide, and traces of 

 silver have been detected by Malaguti and Durocher in Fucus. 



Lead is frequently present. The equally poisonous Thallium has also been 

 found in certain cases. 



The poisonous character of Chromium, Tungsten, Molybdenum, Bismuth, 



1 Wolff, Aschenanalysen, 1871, pp. 134, 136; Church, Proc. Roy. Soc. London, 1888, Vol. XLIV, 

 p. 121 ; Berthelot et St. Andre, Compt. rend., 1895, T. cxx, p. 288; Yoshida, Bot. Jahresb., 1890, 



p. 50. 



3 The analyses given by Wolff (1. c.) are not quoted in detail among the following references. 

 Manganese: Ebermayer, Physiol. Chem., 1882, p. 795; Maumene, Bot. Jahresb., 1886, p. 81 ; 

 Molisch, Die Pflanze in ihren Beziehungen zum Eisen, 1892, p. 71. Cobalt : Ann. d. Chem. u. 

 Phys., 1855, Bd. XCV, p. 86. Copper: Lehmann, Archiv f. Hygiene, 1896, Bd. xxvn, p. I, and 

 Bot. Centralbl., 1896, Bd. LXVIII, p. 56 ; C. Miiller, Zeitschr. f. Pflanzenkrankh., 1894, Bd. iv, 

 p. 142 ; Otto, ibid., 1893, Bd. in, p. 222 ; Tschirch, Das Kupfer, 1893. Mercury: Ann. d. Chem. 

 u. Pharm., 1864, Bd. cxxvn, p. 248. Silver: quoted by Raulin, Ann. d. sci. nat, 1869, v. sen, 

 T. xi, p. 98. Lead : Tschirch, Das Kup r er, 1893, p. 15 ; Hattensaur, Bot. Jahresb., 1890, p. 48 ; 

 Knop, Ber. d. Sachs. Ges. d. Wiss., 1885, p. 51 ; Nobbe, Versuchsst., 1884, Bd. xxx, p. 416 ; 

 Phillips, Bot. Centralbl., 1883, Bd. xni, p. 364, &c. Thallium : Bottger, Jahresb. d. Agr.-Chemie, 

 1864, p. 99 ; Knop, 1. c., p. 50. 



