BARYTA. [ 



in form, erect or reflexed, with terete nerves ; 

 cells parenchymatous, and, except in certain 

 species, furnished with solitary papillae on 

 the transverse walls on both faces, mostly 

 square or more or less hexagonal; lax or 

 loosish, and densely filled with chlorophyll, 

 or with a persistent primordial utricle, rarely 

 thickened. Capsule with a long neck, funa- 

 rioid, pear-shaped or spherical, regular or 

 asymmetrical, straight or variously inclined, 

 smooth or grooved, with an operculum 

 mostly hemispherical or conical, rarely 

 beaked. This family is divided into two 

 tribes : 



MEESIACEJE. Areolation of the leaf 

 lax, smooth, often destitute of primordial 

 utricle (Meesid), or lax and densely papil- 

 lose (Paludella). Capsule erect, elongated, 

 with a more or less elongated neck, hence 

 more or less pear-shaped) smooth, the neck 

 bearing stomata. 



BARTRAMIACE^E. Areolation either lax 

 and smooth, lax and papillose, dense and 

 smooth, or dense and papillose. Capsule 

 erect or inclined, horizontal or pendulous, 

 regular or asymmetrical, smooth or grooved, 

 but more or less spherical, devoid of stomata. 



BARYTA. A knowledge of the crystal- 

 line forms of the salts of baryta is sometimes 

 useful in determining the presence of this 

 substance. 



Eutyrate of baryta (PI. 10. fig. 23). When 

 rapidly separating from an aqueous solution, 

 forms a pearly film upon the surface, con- 

 sisting ot dense aggregations of very trans- 

 parent crystalline laminae, not perfectly se- 

 parable from each other (a). When more 

 slowly formed, stellate groups of crystals 

 are produced (6). The individual crystals 

 are rarely perfect ; and some are so thin and 

 transparent that their outlines are scarcely 

 distinguishable. 



Hydrofluosilicate of baryta (PI. 10. fig. 24). 

 Its production is a test for the presence of 

 baryta. The crystals are scarcely affected 

 by either nitric or muriatic acid. 



Sulphate of baryta (PI. 10. tig. 25). When 

 rapidly formed, consists of crystalline gra- 

 nules (a). When more slowly precipitated 

 from dilute solutions, it consists of very 

 minute stellate foliaceous crystals, somewhat 

 resembling those of the ammonio -phosphate 

 of magnesia (b). See STRONTIA and LIME. 



BASALT. See ROCKS. 



BASEMENT MEMBRANE, of Ani- 

 mals. Is a very thin, transparent, elastic 

 and structureless membrane, lying between 

 the cutis and epidermis of the skin, and be- 



l ] BASIDIOSPORES. 



tween the epithelium and subinucous tissue 

 of the mucous membranes and their pro- 

 longations. It is of considerable firmness, 

 and serves to support the layer or layers of 

 epidermal or epithelial cells. It is not 

 always easily separable and demonstrable, 

 but is perhaps most readily so in the urinary 

 tubules of the kidneys. 



In chemical composition, this membrane 

 mostly resembles elastic tissue. 



BASIDTA. See BASIDIOSPORES. 



BASIDIOMYCETES. A name applied 

 by Sachs to those Fungi which have naked 

 spores situated in a distinct hymenium. 

 See AGARICINI and FUNGI. 



BASIDIOSPORES. The name applied 

 to the acrogenous spores produced in groups, 

 mostly of a definite number, more frequently 

 of four, on the hymenium of many Fungi, 

 the term basidium (sporophore, Berk.) being 

 applied to the four-branched cell upon which 

 they are attached. Basidiospores are pro- 

 duced both by the Hymenomycetous and 

 Gasteromycetous Fungi. In the former 

 they are found upon the external fruit- 

 bearing surfaces, such as the gills or vertical 

 plates of Agarics, on the walls of the tubes 

 of Potyporus, &c. In the Gasteroinycetes 



Fig. 53. 



Development of the basidiospores of 

 Hymenangium griseum. 



they are produced upon the convoluted hy- 

 menium which occupies the interior of the 



Fig. 54. Fig. 55. 



Basidia and basidiospores Basidia and basidiospores 

 of Melanogaster varie- of Octaviana astero- 



gatus. sperma. 



Magnified 400 diameters. 



Fungus in the earlier stages of growth ; and 

 when the spores are mature, the hymenium 



