54 PRINCIPLES OF GARDENING. [CH. II. 



that which is desirable to plants ; and one crop suc- 

 ceeds better after some predecessors than others, be- 

 cause their exuvise is more salutar}'. Upon similar 

 principles is explained the association which, centu- 

 ries since, was first observed to prevail between some 

 plants. Thus, in 1570, Conrad Heresbach wrote thus : 

 " Because there is a natural friendsliip and love be- 

 tween certain trees, you must set them the nearer 

 together, as the "sdne and the olive, the pomegranate 

 and the myrtle." Others, he adds, have a natural 

 hatred, " as the \Tne with the filbert and the bay, &c. ;" 

 and Cato says that the vine is at enmity with the 

 cabbage. 



That some plants are benefited by being grown in 

 the vicinity of others, seems established by obsen^a- 

 tion, and might be rationally expected. Thus the 

 blue bottle {Centaurea cyanus) is rarely found flourish- 

 ing, except in company ^itli a com crop. The bene- 

 fit arising from such associations is probably the con- 

 sequence of the cereal grasses emitting the usual gases 

 in proportions and at times grateful to the Centaurea, 

 or from their excreting something in the soil that is 

 acceptable to its roots. Then, again, the fragrance 

 of the rose is said to be increased by having the onion 

 or some other allium grown in its vicinity. Phillips, 

 in his poem entitled " Cider," alludes to this result : 



" The Paestan rose unfolds 



\ 



Her bud more lovely near the foetid leek, 

 (Crest of stout Britons,) and enhances thence 

 The price of her celestial scent." 



