IN CERTAIN SPECIES OF CARYOPHYLLEÆ AND PLUMBAGINEÆ. 293 
ring in one horizontal plane. These processes, which I consider to be in connexion often, 
if not at all times, with the lateral appendages of the stem, are frequently in Armeria 
maritima of considerable width, and distort the generally more or less central and readily 
recognizable pith materially. In the laxer parenchyma of the medulla of this plant indi- 
vidual cells of very irregular form are found. In Statice arborea, the pith, the cells of 
which are marked by transversely lengthened pits, is vertically traversed by cords of a 
rather thick-walled elongated tissue. In Acantholimon diapensioides the rather compact 
woody mass is singularly lobed in some older stems, as represented in fig. 61, cortical 
inversions penetrating almost to the centre; in Acantholimon (sp. À. tomentello affinis, 
Gr. no. 1589) and Acantholimon (no. 1579), also, the wood is more or less dislocated by 
parenchymatous radial plates or cords ; in the latter species these processes contain many 
much-thickened apparently * sclerogen’ cells. The older wood in various species which I 
have examined presents more or less of a tolerably thick-walled prosenchyma. In Acan- 
tholimon (No. 1589) this tissue occurs in irregular dense masses, which exhibit a manifest 
disposition in concentric belts, as also a decided radial arrangement, as represented by 
fig. 24 (PL LI). The tissue intervening between the conspicuous cords abounds in vessels 
of considerable diameter, which, as in the other species examined, present * slit-marked * 
walls similar to those observed in Caryophylleæ, &e. 
Perhaps the most interesting point in the histology of the wood of these plants is the 
occurrence of minute, apparently intercellular cavities in the tissue traversed by the 
vessels in Statice arborea and Acantholimon diapensioides. In the latter species I have 
more minutely examined these. In this species the cells of the wood in which the small 
and rather sparingly distributed vessels are immersed, are elongated, presenting a reti- 
culated or spiral arrangement of their secondary deposits; it is between these cells, or 
between them and the vessels, that the very minute slit-like spaces are visible, in a suffi- 
ciently thin section of the wood, when examined with a magnifying power of 300 or 400 
diameters. On the nature of these interspaces I scarcely feel myself competent to offer 
a positive opinion, believing it possible that the eyes of a more experienced phytotomist 
might differently interpret it. I regard them as either very minute intercellular verba 
corresponding in some measure to those of Conifere; or as the much-widened blind ex- 
tremities of the pore-canals which traverse the thickening layers of the enclosing cells,— 
the primary cell-walls between each pair of opposing canals becoming absorbed. 
Note.—The specimens belonging to the genera Acanthophyllum (Caryophylleæ) and 
Acantholimon (Plumbagineæ) which I have examined, have been derived from Griffith 5 
extensive Affghan collections. The names of those which have been clearly determined 
I have obtained from the Hookerian Herbarium, in which some of the species have 
been examined and labelled by Boissier. ; 
To my friend Thos. Atthey, of Cramlington, Northumberland, I desire to acknowledge 
myself much indebted for a valuable series of sections illustrative of these structures, 
which he kindly prepared for the microscope at my request. 
