160 



ALTERATION OF POSITION. 



leaves, of the roots themselves, or even of the fruit, as 

 in the case of the cactus (Baillon) . Care also has to be 



exercised in grafting certain 

 fruit trees not to allow the 

 grafted portion to be too 

 close to the ground, else the 

 scion throws out roots into 

 the soil, and the object of the 

 cultivator is defeated. 



Layering is another garden 

 operation dependent on the 

 formation of these organs, and 



Figs. 73 and 74 show formation of roots from leaves induced by the 

 jirt of the gardener. 



advantage is also sometimes taken of this tendency of 

 some plants to produce roots when injured to reduce 

 the dimensions of a plant when getting too large for 

 the house in which it is growing. By gradually in- 

 ducing the production of new roots from the central 

 or upper portions of the stem, it becomes possible, 

 after a time, to sever the connection between the 

 original roots and the upper portion of the trunk, 

 and thus secure a shortened plant. 



On the subject of adventitious roots, &c., reference may be made to 

 Trecul, * Ann. Sc. Nat.,' 1846, t. v, p. 340, et vi, p. 303. Duchaitre, 

 'Elements de Botanique,' p. 219. Lindley, 'Theory and Practice of 

 Horticulture.' Thomson's ' Gardener's Assistant,' pp. 374, et seq. ; and 

 any of the ordinary botanical text-books. 



Formation of adventitious buds on roots. One of the charac- 

 teristics by which roots are distinguished from stems 

 in a general way consists in the absence of buds ; but, 

 as is well known, they may be formed on the roots 

 under certain circumstances, and in cortniTi ])lants, e.g., 



