﻿574 Halsted : Starch Distribution 



In the course of twenty-four hours the portion of the bleached 

 leaflets containing starch were indicated by a darker tinge than 

 elsewhere. A longer exposure to the iodine brought out the 

 starch so that it was located distinctly, and it was found that, with 

 the specimens employed, the starch was confined almost exclusively 

 to the mildewed patches and the neighboring small angular areas 

 that adjoin the portions that already showed the Peronospora. 



The darkening at these diseased patches was sufficient so that 

 a sun print was taken of a leaflet and afterwards enlarged to five 

 times its natural size, as was shown in a photograph. The origi- 

 nal picture was made by placing the leaf directly against the sen- 

 sitized plate so that every detail is exactly as in the leaf, both as 

 to size and position of all parts. 



It is to be remembered that the blanching was not complete, 

 and the iodine, while coloring the starch blue, also tinged the other 

 portions of the tissue of that peculiar "dirty yellow" that is al- 

 ways the bane of the photographer. In short, the picture in this 

 instance, as in all others, is only a faint record of what may be 

 seen when looking at the treated specimen. 



One of the most interesting of the observations made under the 

 subject in hand was with Synchytrium decipiens Farl. in the leaves 

 of hog-peanut, Falcata comosa (L.) Kuntze. 



It will be remembered that the Chytridiaceae to which our sub- 

 ject belongs is without hyphae and, therefore, the locality of the 

 fungus is easily determined by that of the infested cells. The leaf- 

 lets of this host are thin and the iodine easily penetrates the tissue 

 and for the same reason the starch, even when in small amounts, 

 can be distinctly seen. 



In the dozen or so of leaves examined it was found that the 

 starch is located immediately around the spore cysts and extends 

 from it through usually one mesh or irregular area made by 

 the ultimate ramifications of the vascular framework. As a matter 

 of fact the fungus is generally located along the lateral veins of 

 the leaf and these are brought out as irregular blue lines when the 

 leaves have been subjected to the iodine test. When a leaflet is 

 quite badly diseased with the Synchytrium it will take a blue color 

 throughout all its tissues. 



A leaf of Amarantus retrofit 



