622 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Histolog"y of stem of Nyctagineae.* — M, O.-G. Petersen has in- 

 vestigated the minute structure of the stem in this order of flowering 

 plants, especially in the genera Boerhaavia, Sougainvillea, Pisonia, and 

 Neea. The foliar fibro-vascular bundles are not formed from any 

 preceding jirocambial ring, as in Mesemhryanthemum. In the 

 Nyctagiueas this ring is formed outside the young bundles, and is 

 separated from them by several layers of parenchymatous cells. In 

 its interior are developed secondary vascular bundles, as well as a 

 cambial ring composed of cells juxtaposed in a radial manner. The 

 development of this cambial ring varies greatly. Sometimes it forms 

 a large number of medullary cells between the vascular bundles, 

 causing the medulla apparently to assume a larger size ; in other cases 

 it begins at once to form wood-cells. The resulting secondary woody 

 layer varies in appearance in the different genera. The groups of soft 

 bast scattered through the wood consist partly of cambiform tissue, 

 partly also of sieve-tubes, the latter especially in Mirabilis and 

 Oxyhainlius. The primary cortex presents no unusual character. It 

 has no protecting sheath ; collenchyma is generally found in it, but 

 the author failed to detect sclerenchymatous cells. Cork is sometimes 

 formed in the layer of hypodermal cells, as in Pisonia and Boerhaavia, 

 sometimes at a greater depth, at various distances from the epidermis 

 in the same stem, as in Neea parvijiora. 



Secreting Intercellular Passages and Cystoliths in Acantha- 

 cese.t — Eussow confirms the statement by Liborius of the presence of 

 a reddish-brown secretion, rhinacanthin, in the ordinary intercellular 

 passages of Bliinacantlms communis. In the intercellular passages of 

 the root-stems and leaves of Justicia picta he also finds a secretion 

 consisting of small dark red or blackish-brown roundish granules. 

 The secretion of 3Iyrsine africana and Ardisia crenulata was insoluble 

 in sulphuric acid, but soluble in dilute potash, with a beautiful violet- 

 blue passing over into a dirty violet-brown colour. 



Cystoliths were found by Eussow to be widely distributed in the 

 internal tissue, especially in the root of Acanthaceae. They are conical 

 or needle-shaped, and, in Justicia picta, Fittonia gigantea, and San- 

 chezia picta, often attain the length of 1 • 6 mm. Their connection 

 with the cell-wall aj)pears to cease at a very early period. According 

 to the species, they were found in the fundamental and epidermal 

 tissue of the root, stem, or leaves ; in some species they were altogether 

 wanting. The parenchymatous tissue of the Acanthaceae is also very 

 rich in needle-shaped crystals of calcium oxalate, not, however, 

 grouped in bundles like raphides, but distributed irregularly and in 

 inverse proportion to the cystoliths. 



In the stem of Hexacentris coccinea the author found very peculiar 

 needle-shaped cells lying detached side by side within certain cells of 

 the soft bast, bearing an external resemblance to raphides, but with 

 a distinct cell-cavity, and coloured blue by chlor-iodide of zinc. When 



* Bot. Tidsskrift, iii. (1879) pp. 149-76 (2 pis.). See Bull. Soc. Bot. France, 

 xxvii. (1880) p. 166. 



+ SB. Dorpat. Natuif. Ges., 1880, pp. 308-16. See Bot. Centralbl., v. (1881) 

 p. 365. 



