THE VEGETABLE KINGDOM. 427 



compels them to approach each other they languish or die. 

 The flax-plant, for instance, seems to have a manifest an- 

 tipathy for the scabious (Scabiosa arvensis, Linn.). 



At the present time these peculiarities are explained by 

 assuming that the roots emit products favorable to certain 

 species and hurtful to others, products which Plenck, 

 with all the coarseness of one of Moliere's doctors, called 

 the " excrement of plants." 



Duhamel, when having some elms cut down, had already 

 noticed that the soil in which they had stood had under- 

 gone a certain alteration, having become unctuous. 



A Genevese observer, M. Macaire, went even further. He 

 observed that when roots of chicory or Euphorbia were 

 placed in water they exuded into it a colored extractive 

 matter, which could only be an excretion. 



Lastly, Brugmans, professor at the University of Leyden, 

 pushed the matter still further. Having collected this sub- 

 stance from the roots of violets which he had placed in 

 pure fine sand, he found that it acted like poison upon other 

 plants. 



Thus the cause of those curious instinctive mutual ad- 

 vances, already perceived by Mathiolus, who called them 

 the friendships of plants, is demonstrated. Indeed, the old 

 botanist, in his work, says that there is so much affection 

 between the reed and the asparagus that if we plant them 

 together both will prosper marvellously. 



In Germany, agriculture, guided by science, has learned 

 to profit from these mutual affections, and Schwerz, in his 

 learned works, points out how cereals should be allied in 

 order to augment the produce of our fields. 



