252 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



form size, and their nature and function are still left in ob- 

 scurity. 



At a recent meeting of the Linnsean Society, Mr. Francis 

 Darwin read an account of some microscopical researches on 

 the glandular bodies on Acacia spcerocephala and Cecropia 

 pellata, serving as food for ants, and first mentioned by Mr. 

 Belt in his " Naturalist in Nicaragua." In Acacia were two 

 kinds of glands (a) nectar-secreting glands at the base of 

 the petiole; (b) small, flattened, pear-shaped bodies, which 

 tip six or seven of the lowermost leaflets of the bipennate 

 leaves. In Cecropia cylindrical bodies are developed in flat 

 cushions at the base of the leaf-stalk. The structures are 

 homologous in kind cellular protoplasm and contain oil 

 globules, stores of nutriment which undoubtedly the ants 



live on. 



MICROGEOLOGY AND MINERALOGY. 



The anniversary address of H. C. Sorby, President of the 

 Royal Microscopical Society, delivered February 7, is mainly 

 devoted to the application of the microscope to geology. 

 The object-glasses used must be of comparatively small an- 

 gle, e. g., a one eighth of 75 ; large angles are positively det- 

 rimental, not only causing the object to be almost, if not 

 quite, invisible, from the absence of any dark outline, but the 

 focal point of such lenses is so near their front surface that 

 it is quite impossible to penetrate sufficiently deep down to 

 see the minute fluid cavities in the centre of grains of sand, 

 or to reach the fine particles lying on the surface of the 

 glass slip below the thickness of balsam necessitated by the 

 presence of large grains of sand. 



In a paper read before the Royal Microscopical Society, 

 April 4, 1877, by A. Renard, on the " Mineralogical Compo- 

 sition and the Microscopical Structure of the Belgian Whet- 

 stones," the author states that they owe their excessive hard- 

 ness to garnet, instead of finely divided quartz, as hitherto 

 supposed ; in fact, they contain scarcely any quartz. Thin 

 sections seen by transmitted light show myriads of globular 

 forms so excessively minute that their regular bounding lines 

 and frequently lozenge-shaped faces are not attacked in the 

 polishing process. Sometimes they are gathered together 

 at one point; again, they form lines, or chaplets, or are iso- 

 lated. These minute rhombo-dodecahedral forms, or globular 



