154 University of California Publications in Agricultural Sciences [Vol.3 



Little can be said of the mercuric chloride ferric sulphate series 

 given in table 25. Growth is uniformly low throughout, with con- 

 siderable variation between duplicate cultures. The percentage of 

 magnesium is very high in the roots and while less in the tops, is 

 much above that of the control. The percentage of calcium is uni- 

 formly low in both tops and roots. Attention is called to the fact 

 that no iron could be determined quantitatively, except in the highest 

 concentration of salts used. This condition is striking when the 

 rather large amounts of ferric sulphate in the solution are considered. 



A short series is reported in table 26 in which the toxic effects 

 of mercuric chloride when used alone, are evident. There is a de- 

 crease in growth with increasing concentration of the added salt and 

 also an increasing percentage of both calcium and magnesium found. 

 The very low ash content given by the plants in this series is of 

 interest and will be discussed below. 



External Appearances of the Plants 



It seems worth while to note here a few of the more striking 

 appearances of the plants. Since iron salts were purposely excluded 

 from all solutions except those in which it was planned to study their 

 effects, the control plants were of a more or less yellowish green color. 

 Aside from this no differences were noted between control plants 

 grown wdth or without the addition of a little ferric phosphate to 

 the nutrient. 



In every series in which growth was limited by the presence of 

 magnesium salts the roots were short and much thickened. With a 

 high concentration of magnesium in a balanced solution, this effect 

 was not noted however. High concentrations of magnesium were also 

 apparent from the decided yellowing of the older leaves. Excessive 

 amounts of calcium were characterized by the appearance of brown 

 spots or streaks on the leaves. 30 



AVhen any considerable growth was permitted the plants grown in 

 solutions of copper salts were dark green in color. 31 "Where growth 

 was good the roots were apparently normal. In several of the higher 

 concentrations used, copper hydroxide was deposited upon the roots, 

 especially about the tips. A suggestion is made that possibly copper 

 may replace iron as a catalyzer in connection with the building or 

 activation of chlorophyll. 



so Jost, Plant physiology (Oxford, Clarendon Press, 1907), p. 85. 

 si Qniv. Calif. Agr. Sci., vol. 1 (1917), pp. 495-588. 



