362 Gibson . — On Siliceous Deposit in the 
origin, viz. the first appearance of the deposit is over the 
vertical walls of the cells of the innermost layer of the cortex. 
The knife-blade form of plate is by far the most frequent, 
though occasionally the double-wedge form is to be 
met with. 
In older stems the deposit is on the whole extremely 
regular, and consists of ragged, much-elongated bands, which 
anastomose frequently, leaving gaps between for the exit 
of trabeculae. Fig. 8 shows this feature in the siliceous 
lining in the main stem after treatment with concentrated 
sulphuric acid. 
The full-grown plant has a well-marked primary axis, 
quite unbranched for a considerable distance, finally deli- 
quescing in a flabellate manner into a number of secondary 
axes. At the point of origin of a branch the mineralization 
is much more irregular. Fig. 9 shows a portion of the 
deposit in such a situation after treatment with sulphuric 
acid. The silica runs up the trabecular cells and is deposited 
also between the cells of the compound trabeculae. 
The cells of the inner cortex are long and sclerotized, have 
narrow lumina and run longitudinally. The cortical cells 
of the trabeculae also run in a creeping manner along the 
cortical wall before crossing the lacuna. In section the 
silica is found to penetrate between these cells, so that 
the trabecular cell as it leaves the cortex is encased by the 
mineral. Fig. 10 shows a section of the cortex next to 
the lacuna, where it will be seen that the silica is in places 
pierced by apertures through which run the creeping cortical 
cells. Silica may also be distinguished in the minute 
intercellular spaces between the cortical cells. 
S. Griflithii, Spr. 
The siliceous deposit in this species has similar characters 
to that in 5 . grandis , although it is much smaller in amount. 
The plates in the adult stem are not so regular, but the 
cortical trabecular cells are, at their origin from the cortex, 
encased in Si 0 2 . 
