342 PHYSIOLOGY OF NUTRITION. 



1 On some of the points here referred to see Strasburger's Practical Botany. 



2 See Hansen, Verhandlungen der Pliysicalisch-medicinisclien Gesellschaft zu 

 Wiirzburg, Neue Folge, Bd. 18, No. 7. 



3 Respecting the anatomical structure of Brazil wood, see Wiesner, Rohstoft't' 

 des Pflanzenreiches, 1873, p. 555. 



136. Micro-chemical Tests for Alkaloids and Some Other 

 Substances. 



It is well known that in the tissues of the most different plants 

 there are present alkaloids, glucosides, or other substances, re- 

 garding the physiological significance of which little is up to the 

 present known. Many of these bodies, there is no doubt, serve 

 as a means of protection against injurious animals ; others also 

 (e.g. glucosides), under particular conditions, may decompose and 

 yield plastic material (sugar) ; but all these relations have as yet 

 been but little studied. Similarly, the micro-chemical reactions 

 which have been employed for the detection of at least some 

 alkaloids and glucosides in plant tissues, are still in some cases 

 rather uncertain, as I have frequently found. Nevertheless, a 

 few reactions may here be mentioned, and we shall find that the 

 substances in question are at least frequently collected especially 

 in the peripheral tissues of the organs or in the neighbourhood of 

 the vascular bundles, as might be expected if they function as a 

 means of protection against animals. 1 



If we examine a thin section from the horny endosperm of the 

 seed of Strychnos nux vomica, the cells are at once seen to be 

 rather thick- walled. Their contents are proteids, sugar, and fatty 

 oil. If thin sections from the dry seeds are mounted in a drop of 

 concentrated Sulphuric acid, the cell contents in the course of a 

 few minutes take on a reddish colour. We now add to the 

 section lying in Sulphuric acid a fragment of Potassium chromate r 

 cover with a cover-glass, and observe under the microscope. The 

 cell contents, especially those of the endosperm cells immediately 

 below the testa, rapidly take on a beautiful violet coloration, 

 while the cell- walls remain uncoloured (strychnine reaction) . 2 



In transverse sections from the stem or branches of Berber-is 

 vnlgaris (we may, e.g., use pieces from twigs about 6 mm. thick) 

 we easily distinguish the cortex a and the vascular bundles. In 

 the cortex, the soft bast, and the phloem rays, appear many cells 

 with yellow contents, i~he colour being due to the presence of 



