46 PHYSIOLOGY OF NUTRITION. 



blue coloration. In experiments made by myself with leaves of 

 Tropeeolum, this came out very beautifully. 



To determine microchemically whether starch is present or 

 absent in the organs of assimilation, the material (e.g., filaments of 

 algce or delicate transverse sections of leaves, etc.) is first laid in 

 strong warm alcohol, in order to extract the chlorophyll. The 

 bleached preparations are placed in a fairly strong solution of 

 potash, either for a short time in a hot solution, or for twenty 

 hours in a cold solution, carefully washed with water, treated with 

 dilute Acetic acid so as to completely neutralise the potash, once 

 more washed with water, and then mounted in a drop of iodised 

 Potassium iodide solution (prepared by dissolving 0'05 gr. Iodine 

 and O2 gr. of Potassium iodide in 15 gr. of water.) 2 The follow- 

 ing method of detecting starch in green cells is also very con- 

 venient. 3 The research objects (with special success I used quite 

 unprepared leaves of Elodea canadensis and Furiaria hygrometrica) 

 are either at once, or as is often necessary after extraction with 

 alcohol, laid on the slide in a drop of chloral hydrate solution (5 

 parts of chloral hydrate to 2 parts of water) treated with iodised 

 Potassium iodide solution, and at once observed. The chlorophyll 

 is dissolved, the starch grains swell up somewhat, and they as- 

 sume in contact with the Iodine solution a beautiful blue colora- 

 tion, like starch-containing material placed in contact with the 

 Iodine reagent after treatment with potash and dilute Acetic 

 acid. 



If we desire to satisfy ourselves that the starch formed by as- 

 similation is not present in any part of a cell but in the chlorophyll 

 bodies, we may select for examination Spirogyra, Zygnema, or 

 leaves of Funaria hygrometrica, and avail ourselves of the last 

 used method, with chloral hydrate. 



1 See Sachs, Arbeiten des botan. Imtitnts in Wilrzbitrg, Bd. 3, p. 1. 



2 See B6hm, Sitzungsberichte d. Akad. d. Wiss. zu H'ien, Bd. 22, p. 479, and 

 Sachs, Botan. Zeitung, 1864, p. 291. 



3 See A. Meyer, Das Chlorophyllkorn, 1883, p. 28. 



15. The Products of Assimilation, 



There is no doubt whatever that starch always appears in the 

 leaves of many plants as the first easily visible product of assimi- 

 lation. On the other hand there are plants which under very 

 favourable conditions for assimilation produce only comparatively 



