50 
HISTOLOGY OF VEGETABLES. 
When the stems are rubbed together, a grating noise is 
heard, as if they were composed of glass. In the 
Grammacece , especially the canes, silica is also very 
abundant, but is by no means limited to this order of 
plants. It is contained principally in the cuticle and in 
the various structures that are developed from it, such as 
hairs, spines, &c. ; but in some instances layers of cells 
lying much deeper than those of the cuticle also abound 
in silica, and it may be met with in woody fibres and in 
spiral vessels. 
In certain of the canes, as the bamboo, silica some- 
times collects in large solid masses in the interior of the 
joints, forming the substance called “ tabasheer.” It 
would seem that in this case, the silica should be viewed 
in the light of a secretion, as it is poured out in a liquid 
state into the cavity of the bamboo, and I possess a 
specimen in which a spiral vessel, lying in the cavity 
of the joint, has been entirely surrounded by the taba- 
sheer. 
It is generally known that after the burning of hay- 
stacks, masses of irregularly-shaped, but perfectly formed 
glass, are always to be found among the ashes ; these 
result from the fusion of the silica contained in the 
cuticle of the hay, in combination with the potash of 
the vegetable tissue, by which a silicate of that base 
(or glass) is formed. 
In a portion of the bark of a tree from Ceylon, the 
name of which I have never been able to ascertain, the 
