WASTE PRODUCTS OF PLANTS. 117 



circulating fluids of waste materials, than that of actual ex- 

 cretion as seen in the animal forms, which will be considered 

 farther on. There is, however, a sufficiently copious excretion 

 of the respiratory waste product, carbonic acid, in plants, and 

 in addition to this, oxygen. These are too well known to 

 require further comment here. 



There is, also, a true excretory function performed by the 

 roots of plants, and by the seeds in the process of germination. 

 "When barley, or other grain, is caused to germinate in pure 

 chalk, acetate of lime is uniformly found to be mixed with 



it, after the germination is somewhat advanced 



In this case the acetic acid must have been given off (excreted) 

 by the young roots during the process of the germination of 

 the seed." (Vide Johnston's Agricultural Chemistry, 

 page 81.) 



This well authenticated fact may be regarded as the foun- 

 dation of the theory that plants are endowed with the power 

 of excretion. It is supported by the authority of Decandolle, 

 and the convincing experiments of Macaire, although the ex- 

 periments of others have shown that this excretion is limited 

 to very small amounts of matter. Macaire seems to have 

 found opium in the soil in which the poppy plants grew. He 

 also found, in washing the soil with pure water, that it yielded 

 a considerable quantity of acetic acid and a trace of a brown 

 organic matter. 



Liebig devotes considerable space to this, in his agricultural 

 chemistry, with especial reference to the possible effects of 

 these excrementitious substances on the rotation of crops. 

 Other chemists have also occupied themselves with it, and 

 while it has been definitely shown that in some special cases 

 plants may eliminate a sufficient quantity of excrementitious 

 matter to prove injurious to successive generations growing in 

 the same soil, the rule is that poisoning from this cause is not 



