158 ALTERATION OF POSITION. 
this kind in the possession of the writer, and taken 
from a cavity in an apparently solid block of rosewood ; 
externally there were no marks to indicate the existence 
of a central space, but when the block was sawn up 
for the use of the cabinet-maker, this root-like struc- 
ture was found in the centre and attached to one end 
of the cavity. 
The production of roots which ultimately serve as 
props to support the branches, or as buttresses to com- 
pensate for the mcreasing weight of branches and 
foliage, is also a famihar occurrence. The huge gnaurs 
and burrs met with occasionally on some trees often 
produce great quantities, not only of adventitious 
buds, but of roots also. 
The leaves, equally with the stems, have the power 
of emitting roots under certain conditions, as when the 
leaves are in close contact with moist soil or as the 
result of injury. This happens in some plants more 

Fig. 71.—Production of adventitious roots from leaf stalk of celery. 
readily than in others—Bryophyllum calycinum is a 
well-known instance. Mr. Berkeley has described the 
formation of roots from the fractured leaves of celery,’ 
= a = ~ 


1 ‘Gard. Chron.,’ 1852, p. 51. 
