CONCLUSION OF VEGETABLE TISSUES. 
Ill 
tents, such as milky juice, oil, resin, gum, were then 
mentioned, and separately described. Another product 
of cell-secretion is always found in a crystalline state, 
and known by the name of raphides. These are of 
various forms, sometimes occurring as single crystals, 
but more frequently in stellate masses of oxalate of lime 
in the Rhubarb , or in needle-shaped crystals of phosphate 
of lime in the Squill. 
Another inorganic material, found principally com- 
bined with the tissue of the walls of cells, is silica, which 
I described as being so intimately blended with these 
tissues in certain plants, as to form a perfect cast of 
their original structure when all the soft vegetable matter 
has been removed ; abundant examples of this being 
easily obtained from the Grasses and Canes. 
I then exhibited a series of preparations in which 
sclerogen or hard tissue, approaching bone in many of 
its characteristics, occurred as a cell-content, but in no one 
case was a cell entirely occupied by it, a central cavity, 
with a system of radiating pores being always present. 
The last product of cells which I mentioned consisted of 
Phytozoa, or plant animals ; these being found in the 
Char a vulgaris , in Mosses , Ferns , Conferva ?, &c. Each 
cell of the antheridia of some Mosses is occupied by a 
spiral filament which exhibits a peculiar gyrating motion, 
precisely similar to that of the spermatozoa in animals, 
to which they are no doubt analogous. 
The aggregation and modification of the cells pre- 
viously described, make up the entire structure of all 
