359 
Cortex of Selaginella , Spr. 
Cracks very soon appear on the thickened edge, passing 
inwards towards the centre of the adjoining cell, often 
bifurcating or branching irregularly as they go. The thin 
edge very often, even in the young condition, extends quite 
across the cell. If a development of the second type of plate 
occurs on the same cell from both or all sides, the deposits 
may become continuous in the centre of the cell area. The 
very youngest condition of the deposit I have been able to 
detect give the appearance of exceedingly delicate rods lying 
just over the vertical cell- walls. I have never seen the plates 
begin from the centre of the cell-area. 
An examination of many sections taken from different parts 
of the stem leads one to the conclusion that the cracks are 
secondary in origin, and that the differential growth of the 
cortex obliterates in time the evidence of the mode of origin 
of the plates. It will be seen that in Fig. i the plates bear no 
relation whatever to the vertical cell-walls, whilst in Fig. 3 
the relationship is obvious. A comparison of the size of the 
superficial cortical cells renders this still more apparent. 
If a suitable section be boiled in concentrated sulphuric acid 
the organic matter is destroyed, but the plates remain quite 
uninjured. Figs. 4 and 7 show several forms of plates — Fig. 4 
from a young stem, Fig. 7 from a mature stem. The trabeculae 
must of necessity be formed before the commencement of the 
deposition. The deposit, indeed, completely surrounds the 
base of the trabeculae, but does not, at least as a general rule, 
run up them. Fig. 7 represents a large plate from a mature 
stem, showing two apertures through which trabeculae passed 
in the fresh condition. 
With regard to the chemical nature of the deposit there 
cannot be a difference of opinion, although it is not quite 
so easy to feel certain as to its mode of origin and deposition. 
The plates are undestroyed by concentrated hydrochloric, 
nitric, or sulphuric acids, hot or cold. They are unaffected 
by heating to redness. They cannot be stained, and they 
remain after the sections have been treated with cupric 
ammonium hydrate. All these negative reactions point to the 
