ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 225 



y. General. 



Mosaic Disease of Tobacco.* — Herr C. J. Koning, after alluding to 

 the great infectiousness of the disease, remarks that the anatomical 

 changes in the earlier stages of the disorder are extremely slight. At 

 first dark bluish-green streaks and vesicles appear, while later on the 

 chlorophyll-granules break up and the cell- walls disappear. From the 

 fact that the virus, even in minimal doses, easily reproduces the disease 

 in healthy plants, it seems a fair conclusion that the exciting cause of 

 the disease is a micro-organism ; but even under the highest powers none 

 were to be detected, and numerous cultivation experiments on different 

 media were entirely negative. Hence there seems to be some resem- 

 blance in these respects to the virus of rabies and that of foot-and-mouth 

 disease. 



Megaloxylon, a new Genus of Fossil Vascular Plants.f — From a 

 collection of fossil plants from the Coal-measures, Mr. A. 0. Seward de- 

 scribes one which he regards as the type of a new genus of Cycadofilices 

 forming a connecting link between the Paleozoic forms and recent ferns. 

 The stem is probably monostelic ; the primary wood consists of tracheids 

 with multiseriate polygonal bordered pits, and parenchyme ; the secon- 

 dary wood is of the Cycadean type, with broad medullary rays ; the 

 exarch leaf-traces consist of long tracheitis associated with xylem- 

 parenchyrne ; each leaf-trace traverses the peripheral region of the stele 

 through several internodes, and finally passes through the secondary wood 

 in an obliquely horizontal direction. 



Calamodendreae.J — Herr B. Eenault regards the fossil Calamoden- 

 dreae as most nearly related to the Gnetacese among existing forms, being 

 intermediate between them and the cryptogamic Calamariaceae. The 

 following is given as a diagnosis of the order : — Stem jointed ; xylem- 

 bundles separated by more or less broad primary medullary rays ; 

 secondary or xylem-rays composed of cells which are higher than broad ; 

 ends of the xylem-bundle usually with a lacuna on the pith-side ; secon- 

 dary xylem radiate ; cambium-zone distinct in the stem, branches, and 

 roots ; branches and roots verticillate. The family comprises the genera 

 Bornia, Arthropitys, and Calamodendron. 



B. CRYPTOGAMIA. 



Cryptogamia Vascularia. 



Epiphytic Ferns. § — Herr K. Giesenhagen proposes to place the epi- 

 phytic forms of the Polypodiaceae hitherto known as the Niphobolus-form 

 in a distinct genus with that name. They exhibit several special points 

 of structure which adapt them to their epiphytic habit. The under 

 side of the leaves is clothed with stellate hairs. Some species have 

 hydathodes in the form of small pits on the upper side of the leaf often 

 filled with calcareous scales. In some species the assimilating tissue 

 on the under side of the leaf has a loose structure, and there is no water- 



* Zeitschr. f. Pflanaenkrankh., 1899, p. 65 (1 pi.). See Centralbl. Bakt. u. Par., 

 2 ,e Abt., vi. (1900) pp. 27-8. Cf. this Journal, 1899. p. 428. 



t Proc. Cambridge Pbil. Soc., x. (1899) pp. 137-74 (5 pis. and 9 figs.). 



J Bull. Son. d'Hist. Nat. Autun, xi. (1S98) (12 pis. and 9 ri-H.). Sue Bot. Oen- 

 tralM., lxxx. (.1899) p. 485. § Festschr. f. Bohwendener, 1899, pp. 1-18 (1 pi.). 



