﻿Starch Distribution as affected by Fungi.* 



By Byron D. Halsted. 



m 



A study of the distribution of starch in variegated leaves led 

 to a consideration of the presence of this carbohydrate in leaves 

 that were more or less affected with parasitic fungi. Thus, from 

 the variegated Abutilon and Ficus leaves it was an easy step to those 

 that were mottled by the presence of fungi. 



The treatment consisted in immersing the leaves in weak al- 

 cohol in glass vessels which stood in the full light of the sun. 



The time required for the removal of the chlorophyll depends 

 ich upon the thickness and density of the leaf and whether it 

 was freshly gathered or a dried specimen. Usually two or three 

 days are sufficient for the blanching of the leaf when it is ready 

 to be placed in a weak solution of iodine made by adding an ounce 

 of the ordinary solution of iodine in iodide of potassium to a pint 

 of water. 



After remaining for a few hours there may be some changes 

 expected, the thinner the leaf the more rapid the reaction. The 

 starch in the leaf responds to the iodine test and, turning blue, 

 brings out the locality where the starch is present in the leaf. 



The first subject to be tested chanced to be some dried leaflets 

 of Potentilla Monspeliensis affected with the Peronospora poten- 

 tillae DeBy., which, somewhat to my surprise, became quite dis- 

 tinctly blue at the areas where the fungus was bearing its conidia. 



This fungus produces angular patches of a brownish color, 

 easily seen from the upper side, while below the surface of the 

 spots become covered with the conidiophores and conidia of the 



ewy 



small 



patches with irregular outlines. 



In this instance the leaflets were first placed in 50 per cent, 

 alcohol in a large culture jar with glass cover and set in the sun. 

 After the green has been removed the leaves were transferred to 

 another culture jar containing the iodine and kept in the dark. 



* Read before Section G, A. A. A. S., at Boston, August 23, 1898 



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