ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 733 



last are derived from the fruits of various species of Medicago, 

 especially M. apicidata, denticulata, and Tenoriana. The uncon- 

 nected bast-fibres are probably from the leaves and epidermis of the 

 stem of Gyncrium argentcum, the most abundant grass in the pastures 

 of Uruguay, Buenos Ayres, Paraguay, and Entre Rios, from which 

 the wool may have come. The animal fibres were entirely wool. 



3. Distinction between fibres of hemp and flax. The bast-cells of 

 hemp and flax present no character by which they can be distinguished 

 with certainty under the Microscope, even with the assistance of re- 

 agents. The bast-cells of flax are slightly more slender, but this 

 cannot be relied on. A transverse section of both is usually circular, 

 but occasionally polyhedral or flattened, and the size of the cavity 

 affords no certain criterion. The formation of layers is slightly more 

 obvious in hemp ; but the difference is too small for practical use. 

 The pores described by Schacht and Wiesner are believed by Cramer 

 to be transverse folds of peripheral layers of cell-wall. Both fibres 

 are coloured blue by iodine and sulphuric acid ; ammonio-oxide 

 of copper causes appearances of swelling in both. Hemp-fibres are 

 not always coloured yellow by sulphate of anilin. The best dis- 

 tinctive character of the two fibres is the substances which accidentally 

 accompany them. The parenchyma which surrounds hemp-bast 

 contains numerous crescent-shaped clusters of crystals of calcium 

 oxalate, which the bast-parenchyma of flax does not. Among the 

 bast-cells of hemp are also elongated cells widened tangentially, 

 filled with an intensely red-brown endochrome, sometimes composed 

 of connected ribbon-shaped masses, sometimes broken up into 

 quadrangular pieces, insoluble in boiling potash, cold alcohol, ether, 

 turpentine-oil, and benzin, offering long-continued resistance to con- 

 centrated sulphuric and hydrochloric acids, and rendered colourless 

 by Schulz's solution. The epidermis of the two plants also presents 

 differences. That of flax has numerous stomata and no hairs ; that of 

 hemp few stomata and unicellular hairs thickened in a warty manner. 

 These characters are always easy of detection. 



The Microscope in Engineering "Work* — The following is a 

 paper by R. Grimshaw, read at a meeting of the Franklin Institute. 



" The specimens shown are intended to outline a method of using 

 the Microscope as an aid to the testing machine in estimating the 

 value of structural materials. While it is not intended to suggest 

 that the Microscope will determine definitely the elastic limit, nor 

 even the breaking strain of structural materials, it is designed to 

 convey very distinctly the idea that the Microscope may be used for 

 preliminary investigations which will determine whether or not the 

 material is good enough to warrant its being tried on the testing 

 machine. If the Microscope condemns the material, it is not worth while 

 going to the expense of having it tested by more expensive methods. If 

 the Microscope fails to reveal any flaw, then the material may be sent 

 to the testing machine to be further proved. The larger the specimens 

 that would be required for testing in the machine, the more marked 



* Journ. of the Franklin Institute, cxiv. (1882) pp. 173-5. 

 Ser. 2.— Vol. II. 3 D 



