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 

Fries. 73 and 74 show formation of roots from leaves induced by the 
art 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 ovadually i 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 ae 
and thus secure a shortened plant. 
On the subject of adventitious roots, &c., reference may be made to 
Trécul, ‘Ann. Sc. Nat.,’ 1846, t. v, p. 340, et vi, p. 303. Duchartre, 
‘Elements de Botanique, p 219, Lindley, ‘Theory and Practice of 
Horticulture.’ Thomson’s He cidcnae 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 certain plants, e.e., 
