Cortex of Selaginella , Spr. 361 
the plant as a soluble silicate of magnesia or of lime, or 
possibly as a double silicate of these bases. (I am greatly 
indebted to my colleague Dr. T. L. Bailey for his aid in this 
part of my work.) 
S. Martensii, var. flexuosa. 
In this variety the deposit on the lacunar wall is very 
well marked and the plates are of considerable thickness. 
The superficial cortical cell-layer alone, however, is well 
mineralized, although here and there the mineral may be 
detected in the minute intercellular spaces between the 
second and third layer of cortical cells. On the other hand, 
the trabeculae are plentifully supplied with Si 0 2 , the plates 
lying loosely round the basal cells next the cortex, and the 
clustered cells of the compound trabeculae have a large 
amount of Si 0 2 in their intercellular spaces. 
S. Martensii, var. variegata. 
In this form the trabeculae are not so much silicified. 
The plates on the lacunar walls are more uniform and 
thinner, but the mineral can be traced into the cortex to 
the third, or even, in some places, the fourth cell-layer. 
S. Martensii, var. stolonifera. 
This variety resembles in all respects, so far as regards the 
siliceous deposit, var .flexuosa, 
S. grandis, Moore. 
I am not aware of any published account of the occurrence 
of Si 0 2 in any species of Selaginella save S. Martensii. 
In examining the fine collection in cultivation at the Royal 
Gardens, Kew, I found that a deposit of the same mineral 
occurred in the cortex of 5. grandis , as well as in the other 
species named above. I propose to give a brief account of 
the essential features shown by the deposit in that form. 
In the first place the deposit is relatively much greater 
in amount than in 5. Martensii or any of its varieties. 
The plates are thicker and more regular in form, but still 
have the same characters so far as regards their mode of 
