540 University of California Publications in AgricvXtural Sciences [\^ol. 1 



a stimulating power of ZnSO^ at still greater dilutions than those 

 which he employed. More direct evidence of the stimulating 

 effects of ZnS04 is given by Kanda'"'^ in solutions free from 

 nutrient salts, and by Javillier'^- in nutrient solutions. So far 

 as solution cultures of all kinds are concerned, therefore, the 

 evidence with respect to the effects of zinc on plants is conflict- 

 ing, it being as strong on the side of stimulation at great 

 dilutions of ZnSO^ as on that of lack of it or of definite toxicity. 

 Let us now examine tlie data available in which a solid 

 substratum such as sand or soil is used instead of the solution. 

 Direct observation of toxicity of zinc to plants in solid media is 

 given by Storp, whose w^ork is above cited, by Noble, Baessler, 

 and Will,^^ Jensch,^* Ehrenberg," and Haselhoff and Gossel.^*^ 

 Evidence of the non-effectiveness of zinc either as a toxic or 

 stimulating agent is given by Phillips," by Holdefleiss,'^''^ and 

 by Haselhoff' and Gossel '^^ As against these results, however, 

 we have many others showing definitely stimulating effects 

 of zinc on plants grown in sand or soil. Among them may be 

 mentioned those of Kanda,*"' Jensen,**^ Silberberg,"- Zaleski and 

 Reinhard,'^ Ehrenberg,''* Bertrand,-'^ Nakamura (with some 

 plants only),"" Javillier,'" Roxas,'"^ Lipman and Wilson,"** and 

 the present writers. While, however, the evidence appears to 



51 Jour. Col. Sci., Tokyo Imp. Univ., 19, p. 1. 



52 Coinpt. EencL, etc., 155, p. 1551. 



53 Landw. Versuchs. Stat., 30, p. 380. 



54 Ztschr. Angew. Cliem., 14, p. 5. 



55 Clieni. Zeit., 32, p. 937. 



56 Ztschr. Pflauzenkrank., 14, p. 193 ; E. S. E., 16, p. 952. 



57 Cliem. News, 46, p. 224. 

 ssLanchv. Versuchs. Stat., 28, p. 472. 



50 Ztschr. Pflanzenkrank., 14, p. 193 ; E. S. K., 16, p. 952. 

 6»* Jour. Col. Sci., Imp. Univ. Tokyo, 19, p. 47. 



61 Bot. Gaz., 43, p. 11. 



62 Bull. Torrey Bot. Club, 36, p. 480. 



63 Biochem. Ztchr., 23, p. 193. 



54 Landw. Versuchs. Stat., 72, p. 15. 

 65Eev. Sci. (Paris), 49, p. 673. 



66 Bull. Col. Agr., Tokyo Imp. Univ., 6, p. 147. 



67 Ann. Inst. Pasteur, 22, p. 720 ; also 7th Internat. Cong. Appl. Chem., 

 sec. vii, Agi-. Chem., p. 163. 



68 Philippine Agric. and Forester, 1, p. 89. 



69 Bot. Gaz., 55, p. 409, 



