356 Gibson . — On Siliceous Deposit in the 
Graf zu Solms; to the Director of the Royal Gardens, Kew ; 
and to the Curator of the Botanic Gardens, Glasnevin, Dublin. 
Of these species I found sixteen to contain a siliceous deposit, 
viz. : .S'. Martensii , Spr. (both the type species and the varieties 
Jlexuosa, compacta, stolonifera and variegatd) \ S.grandis, Moore ; 
S. Griffithii , Spr. ; 6'. inaequalifolia , Spr. ; S'. Lobbii , Moore ; 
S', haematodes , Spr.; S', suberosa , Spr.; S', atroviridis , Spr.; 
S', erythropus , Spr. ; S', bakeriana , Bail. ; S', stenophylla , A. Br. ; 
S', involvens , Spr. ; S', gracilis , Moore ; S', fiabellata , Spr. ; 
S', caulescens , Spr. var. amoena , and S', emiliana. 
In all these the deposit presents the same essential characters ; 
but there are individual differences, more especially in the 
distribution and amount of mineralization. I purpose selecting 
for detailed description and analysis S'. Martensii , Spr., var. 
compacta , A. Br. (a form kindly named for me by Professor 
Dr. Kuhn), and giving a brief account of the deposit as seen 
in the other species. 
S. Martensii, Spr., var. compacta, A. Br. 
Without going into the minute histology of the stem, 
which will be treated of fully in a future paper, it will be 
sufficient to say that the single stele is suspended in a well- 
developed lacuna by trabeculae stretching from the innermost 
layer of the cortex to the pericycle. The external surface of 
the pericycle is covered by a cuticle. The trabeculae are of 
two kinds, simple and compound. The simple type consists of 
usually one, at most three cells; the compound type, which 
is by far the more numerous, of an attaching cell on the one 
side to the pericycle — endodermal cell — on the other to the 
cortex, and between these a cluster of thin-walled swollen cells, 
containing protoplasm, chlorophyll and starch. In the fully- 
developed stem these swollen cells completely fill the lacuna, 
and give it the appearance of a layer of loosely-arranged 
parenchyma, with numerous intercellular spaces. The cortical 
wall of the lacuna is covered by a plentiful deposit of mineral 
matter, laid down apparently in quite irregular colourless plates. 
If a portion of a stout stem be longitudinally sectionized so as 
