46 SCIENCE PROGRESS 



cretionary in origin. Secondary changes due to the local 

 formation of anhydrite are also described. 



The origin of the so-called " glassy meteorites " or tektites 

 is considered by V. Goldschmidt [Zeit. Kryst., 56, 420, 1920). 

 The view of E. Suess [Mitt. geol. Ges, Wien, 7, 51, 1 914 ; H. S. 

 Summers, Proc. Roy. Soc. Victoria, 21, 423, 1909) that such 

 objects as moldavite, billitonite, and australite have had a 

 meteoric origin is adopted and their conditions of formation 

 are considered. The two latter types are supposed to have 

 been in a molten condition with low viscosity, as they possess 

 the typical structure of " drops," the billitonites, however, 

 being assumed to have been formed at a greater height above 

 the earth on account of their greater size and deeper surface 

 erosion. The tendency of moldavites to split off in spherical 

 shells and the occurrence, in them, of elongated fluid inclusions 

 is held to indicate a high degree of viscosity in the molten state. 



The meteoric origin of the tektites is also maintained by 

 C. E. Tilley {Miner. Mag., 19, 275, 1922) on the basis of an 

 investigation of the densities and refractive indices of natural 

 glasses. By plotting the specific refractivity of the glasses 

 against the density, it is shown that the points representing 

 the properties of the tektites lie in a field which is distinct from 

 those of the rhyolitic and trachytic obsidians. The fields of 

 the latter lie at the albite end of the Ab-An curve, while the field 

 appropriate to the basalt glasses lies at the anorthite end of 

 the same curve and in the same region as the series MgSiOg - 

 CaSiOs (c/. E. S. Larsen, Amer. Journ. Sci., 28, 263, 1909). 



BOTANY. By E. J. Salisbury, D.Sc, F.L.S., University College, London. 



Plant Diseases. — F. Mensil (Ann. d. Sci. Nat., Dec.) gives an 

 excellent summary of our present knowledge of the occurrence 

 of organisms allied to the Trypanosomes in plants. Lepto- 

 monas Davidi was first recorded by Lafont in 1909 as occur- 

 ing in the latex of herbaceous species of Euphorbia, chiefly 

 E. pilulifera, which when badly infected become markedly 

 etiolated and eventually wither. 



Artificial inpculation has been successfully accomplished, 

 but in nature infection is brought about by Hemiptera of the 

 genus Stenocephalus . 



An allied Trypanosome has been found to occur in the 

 latex of some Asclepiadaceous plants, and Franchini has re- 

 cently described a similar organism in a member of the Apocy- 

 naceae. The presence of these organisms in plants is probably 

 more or less accidental, but that they should find in the latex 

 a suitable environment is none the less interesting. 



Brown {Ann. Bat., Jan.) finds that water retained on the 



