Relation to Deleterious Chemical Agents 447 



algae. They have been effectively employed by Moore 

 and Kellerman * 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- 

 tion more than half a century ago that plants may influence 



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



