IN CERTAIN SPECIES OF CARYOPHYLLEyE AND PLUMBAGINE.E. 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 ii-regular form are found. In Statice arboreu, 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 AcanthoUmon 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 AcanthoUmon (sp. A. tomentcllo afiinis, 

 Gr. no. 1589) and AcanthoUmon (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-waUed prosenchyma. In Acan- 

 thoUmon (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. 24i (PI. 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 CaryophyUece, &c. 



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 AcanthoUmon 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 ceUs, 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 ^^ more experienced phytotomist 

 might differently interpret it. I regard them as either very minute intercellular cavities, 

 corresponding in some measure to those of Coniferce ; 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 (CaryophyUeae) and 

 AcanthoUmon (Plumbagineae) which I have examined, have been derived from Griffith's 

 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. 



