CH. Il] IODINE METHOD. 19 



cover them^ The solution is now coloured by the 

 addition 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 under the microscope in the leaf examined as 

 a transparent object. 



(26) Variegated leaves. 



Test Sachs' method on a variegated leaf such as 

 that of the ivy 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 a broken line made 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 part corre- 

 spond to yellow stripes in the stained part, and the purple 

 to the green. Twelve hours is necessary for extracting 

 the chlorophyll, and an hour for iodine staining. 



(27) Disappearance of starch in darkness. 



Either of the methods may be tried on submerged 

 water-plants (e.g. Elodea, Potamogeton) which have been 



1 Chloral hydrate 8 parts, water 5 parts. 



2 — 2 



