CH. II ] IODINE METHOD. 23 



solving the crystals in as much distilled water as will just 

 cover them 1 . The solution is now coloured by the ad- 

 dition of a little tincture of iodine, and is ready for use. 

 Delicate leaves, such as those of submerged water-plants, 

 when placed in Schimper's solution, are rendered so trans- 

 parent that every detail of starch-distribution can be 

 studied in the leaf examined as a transparent object under 

 the microscope. 



(26) Variegated leaves. 



Test Sachs' method on a variegated leaf such as that of 

 the ivy (Hedera) or of Arundo donax. In the case of the 

 ivy a rough plan of the green and white parts of the leaf 

 must be traced on paper placed under the leaf, which may 

 best be done by tracing a broken line with a blunt instru- 

 ment dotted along the lines separating the chlorotic from 

 the green parts of the leaf. The iodine-stained leaf is 

 then compared with the plan. With Arundo no such 

 process is necessary, the chlorotic regions are in longi- 

 tudinal stripes, and it is only necessary to cut out of the 

 leaf a short piece, which, after staining in iodine, can be 

 replaced between the base and apex of the leaf to which 

 it belonged : the colourless stripes in the fresh parts cor- 

 respond to yellow stripes in the stained part, and the 

 purple to the green. Both the extraction of the chloro- 

 phyll and the staining with iodine are slow processes in 

 the case of Arundo. 



(27) Disappearance of starch in darkness. 



Either of the methods may be tried on submerged 



1 Chloral hydrate 8 parts, water 5 parts. 



