ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 657 



of the anatomical structure of the genera Mammillaria, Echinocadus, 

 Ecliinopsis, Cereus, Phyllocactus, Ejjiphyllum, Bhipsalis, Ojmntia, and 

 Peireskia. The characters derived from the presence of various kiucls 

 of secretion-receptacles follow, as a general rule, the other characters 

 which distinguish the genera. The species may be divided, from this 

 point of view, into three categories : — those in which crystal-cells only 

 are present ; those which possess both crystal-cells and latex-passages ; 

 and those which have both crystal-cells and mucilage-cells. 



The mucilage-receptacles are always cells, very rarely having the 

 character of passages ; they may contain also separate crystals of 

 calcium oxalate, or sphero-crystals ; they are distinguished from the 

 adjacent parenchyme-cells by their much greater size, and are usually 

 found in the chlorophyll-tissue ; they do not occur in the root. In 

 some species they are found also in the pith ; in the leaves of 

 Opuntia they are scattered through the palisade-parenchyme. The 

 latex-receptacles are confined to species of Mammillaria, where they 

 have the form of a system of passages ; these are of lysigenous, and not, 

 as de Bary states, of schizogenous origin. They occur chiefly in the 

 cortical and palisade-parenchyme, extending also to the root. Crystal- 

 cells are found in all the Cactaceae without exception ; they are usually 

 thin-walled cells containing a single cluster of crystals of calcium 

 oxalate. These are sometimes present in such enormous quantity that 

 they constitute 85 per cent, of the ash, especially in old woody stems. 



The mode and place of formation of the mucilage-cells and other 

 receptacles is described in detail in several species and genera. As 

 regards their physiological function, the author regards the mucilage- 

 cells as serving as receptacles for moisture in dry situations and climates, 

 the latex-passages and crystal-cells as serving to protect from the 

 attacks of animals, and as increasing also the rigidity of the stem. 



Transfusion-tissue of Coniferae.* — Herr G. A. Karlsson has studied 

 the structure of the transfusion-tissue in the leaves of a large number 

 of Coniferee. Finns austriaca may be taken as a type. The cells which 

 surround the true vascular bundles within the bundle-sheath are of four 

 kinds, viz, : — (1) The true transfusion-cells which occupy the greater 

 part of this space : these are isodiametric, and have several circular pores 

 on each of their lignified walls ; on the xylem-side of the bundle they 

 pass gradually into (2) the pith-like transfusion-tissue, the elements of 

 which are very long, with evident intercellular spaces, and minute pores 

 in the thin slightly lignifiel walls. (3) The bast-fibres, often divided 

 by thin septa, forming a plate below the phloem of the bundle. (4) 

 Among the true transfusion-cells are isodiametric elements which may 

 be called transfusion-cells with simple pores, bearing a resemblance to 

 sieve-plates. The xylem of the vascular bundle passes over into the 

 true transfusion-tissue by a tissue which may be called transfusion- 

 xylem, the phloem into the transfusion-cells with simple pores by a 

 transfusion-phloem. The author distinguishes also four types as respects 

 the position of the transfusion cells in the vascular bundle. 



Increase in thickness of the arborescent Liliaceae.j — Dr. P. 

 Eoseler has made a study of the mode of thickening of the stem and 



* Acta Univ. Lund., xxiv. (1887-8) No. 7, 58 pp. and 1 pi. See Bot. Oenfralbl 

 xxxviii. (1889) pp. 7H0 and 756. '' 



t Jabrb. f. WibS. Bot. (Pringsheira), xx. (1889) pp. 2.')2-348 (4 pl^s.). 



