96 



Journal of Applied Microscopy. 



able small flakes and spangles of a 

 slightly brownish yellow color and bril- 

 liant metallic luster. This shows under 

 the microscope a posphyritic structure, 

 the ground mass being composed of a 

 perfectly clear and colorless glass basis. 

 The crystallized portion of the mass 

 consists entirely of copper and may be 

 divided sharply into three distinct 

 groups, large phenocrysts, small pheno- 

 crysts, and microlites which differ great- 

 ly from each other, both In the size and 

 in the habit of individuals. All of the 

 large phenocrysts, which range in diame- 

 ter from .05 mm. to 12 mm., are tabular 

 and extremely thin, the thickness scarce^ 

 ly . exceeding .002 mm., and often less 

 than half this, being perfectly opaque, 

 notwithstanding their excessive tenuity. 

 Most of them are hexagonal in outline, 

 the hexagons being of almost ideal 

 symmetry; and equilateral triangles, 

 which occasionally show truncated 

 angles, also occur. They show a rather 

 yellowish copper color and in reflected 

 light a brilliant metallic luster. 



The faces of these hexagons and tri- 

 angles are in general perfectly smooth 

 and plane, but a number show a pecu- 

 liar appearance (Figs. 1 to 8). In such 

 cases we see that the central part of 

 the face is depressed, forming a very 

 shallow hexagonal or triangular pit, 

 symmetrical with the crystal line, and 

 surrounded by a salient edge about 

 .004 mm. broad, and with sloping and 

 rounded sides. The angles of these 

 shallow depressions are generally 

 rounded, so much so in some cases that 

 they assume an almost circular form 

 (Fig. 2). It may be remarked that such 

 shallow pitted surfaces are not rare in 

 native copper crystals, and quite com- 

 mon in gold. This peculiar form, which 

 seems to be due to a skeleton growth, 

 is always accompanied by projections of 

 greater or less length at the outer angles 

 of the tabular crystals, as shown in the 

 figures. These projections are in gen- 

 eral rounded and show no crystal faces, 

 but in a few cases (Fig. 4) they are seen 

 to be minute octahedra. 



In addition to these more regular 

 forms, some skeleton crystals are to be 

 seen (Figs. 5, 6, 7), which are made up 

 of narrow ridges and show that the pit- 

 like depressions are due to incomplete 

 growth, and not to corrosion. A curi- 

 ous and quite unique form is shown in 

 Fig. 8. This is a "Siamese twin" of the 

 hexagonal tables joined together by a 

 narrow ridge. 



The copper crystals making up the 

 second group are smaller than the pre- 

 ceding, varying from .01 to .03 mm. in 

 diameter, and are not only quite differ- 

 ent in habit, but much more diverse in 

 form. 



The third type, that of twinned forms, 

 while of about the same size, offer much 

 more variety. The twinning plane is' in 

 every case the usual one, an octahedral 

 face, and the twins are either simple or 

 repeated. The simple forms are shown 

 in Figs. 9 and 10. 



The polysynthetic twins are either 

 fivelings or fourlings (Figs. 11 and 12), 

 formed of either five or four octahedra 

 grouped about a common center, the 

 latter showing a re-entrant angle at one 

 side, and the fivelings forming almost 

 symmetrical pentagonel bi-pyramids, 

 since the octahedral angle (70° 32') is 

 almost one-fifth of 360°. 



It seems that the glass is produced 

 by melting together glass, cuprous 

 oxide and some reducing agent, such as 

 siderite, Fe CO3, and that Fe O is in 

 this case the reducing agent is shown by 

 the greenish color of the imperfect 

 glass, which is not the blue-green of 

 copper, but the yellow-green of ferrous 

 glass and perhaps due to too large a 

 quantity of reducing agent. 



Rot Hopping. 



New York. 



The Aseptic Cultivation of Mycetozoa. 



As supplementary to Dr. Ayers' article 

 on "Methods of Study of the Myxamoe- 

 bae and the Plasmodia of the Myce- 

 tozoa," published in the January number 

 of this journal, a brief review of Dr. 

 Casper O. Miller's paper with the above 

 title, published in the quarterly Journal 

 of Microscopical Science, vol. 41, part 1 

 (March, 1898), 29 pp., 2 pi., may be of 

 interest. 



This investigation was undertaken in 

 the course of a study of the kinds of 

 protozoa which are found in the air. 

 According to the critical portion of his 

 paper. Miller appears to have developed 

 the most elaborate method of studying 

 the mycetozoa yet brought forward. The 

 method would seem to promise " pure 

 cultures," yet he says, "Bacteria are 

 found in all the cultures," and promises 

 in a future paper to discuss their influ- 

 ence upon the growth of mycetozoa. 

 The following species were cultivated: 

 Physarum cinereum, Stemonitis sp., 

 Chondrioderma difforme, Didymium 

 microcarpum and Aethalium septicum. 

 The spores of these were planted in the 

 culture medium and the course of devel- 

 opment traced from the Zoospores to the 

 formation of Plasmodia, and finally the 

 production of sporangia. After trying 

 several methods, the author finally 

 decides upon the following as the best: 

 A handful of hay is placed in a jar and 

 washed repeatedly until the water 

 remains colorless. It is then covered 

 with fresh water and allowed to soak 



