Relation to Deleterious Chemical Agents 447 



algse. They have been effectively employed by Moore 

 and Kellerman 1 for the eradication of such organisms in 

 ponds and water supplies. For this purpose copper sul- 

 fate is used at the rate of 1 part to 250,000-1,000,000 

 parts of water. A copper coin in a small dish of water 

 containing half a dozen threads of a green alga is sufficient 

 to cause death in a day or two. 



270. Formalin. - - Formalin is a penetrating toxic agent 

 for all plant cells. According to Clark it ranks close to 

 mercuric bichlorid and silver nitrate as a poison for fungi 

 in beet decoction. In agricultural practice formalin so- 

 lutions are important in the control of certain fungous 

 diseases by seed treatment. The seed do not absorb the 

 solution so rapidly as the spores, so that a short immersion 

 may serve to disinfect the former. Formalin is employed 

 for the prevention of bunt of wheat, loose smut of oats, 

 and potato scab. 



271. Organic bodies. - The effects of various alkaloids 

 and other nitrogenous bodies upon the higher vertebrates 

 have long been a matter of experimentation. The toxic 

 products of disease-producing bacteria are of this nature. 

 Such substances are frequently more toxic to organisms 

 possessing complex nervous and circulatory systems ; but 

 similar substances may be injurious to protoplasm in gen- 

 eral. Through the decomposition of animal or vegetable 

 matter in the soil, toxic bodies may be formed, and these 

 may at times play a recognizable role in the relations of 

 vegetation. 



272. Root excretions. - - De Candolle made the sugges- 

 t ion more than half a century ago that plants may influence 



1 Bureau Plant Ind., U. S. Dept. Agl., Bui. 64 : 44 pp., 1904. 



