﻿AS AFFECTED BV FUNGI 577 



appearance after they have been in iodine for a few minutes. The 

 ordinary wood of the gall-bearing twigs show with the same treat- 

 ment only a small amount of starch, not enough to appear even 

 bluish to the eye after being treated with iodine. 



There are certain species of fungi that cause an upright growth 

 of the host when normally the stems are prostrate or reclined. The 

 purslane plants affected with Cystopus portulacae (DC.) are a case 

 in point. An examination has been made of the upright, usually 

 dwarfed and badly infested stems of the Portulaca oleracea as com- 

 pared with similar portions of the healthy and prostrate branches. 

 In the latter it is noted that there is much more pink coloring in 

 the sap of the epidermal cells of the upper than the lower side and 

 a larger amount of chlorophyll in the exposed than in the shaded 

 half of the stems as they lie upon the ground. The wood zone is 

 much nearer the outside upon the upper than the lower half of 

 the stem, but there seems to be no marked difference in the wood 

 zone itself, which is circular or oval in outline, consisting of a broken 

 ring of 1 5 to 20 vascular bundles. 



In the healthy stem, while the starch is scattered somewhat, it 

 is confined quite closely to a thin layer of small cells just outside 

 of the ring of wood. The upright mildewed stems have less 

 chlorophyll present, but aside from this the most noticeable differ- 

 ence is the fact that the starch zone is indistinct, the granules 

 being distributed in the cells of the parenchyma both within and 

 outside the starch -bearing sheath so distinctly differentiated in the 

 healthy stem. 



In sections made of turnips suffering from the club root fungus, 

 Plasmodiophora brassicae Wor., it was quickly observed that the dis- 

 eased portions were quite generally starch -bearing. Thin sections 

 treated with iodine demonstrated to the eye and the compound mi- 

 croscope that the main portion of the starch is contained in the cells 

 infested with the slime mould. Sections of the same turnip taken 

 in its healthy portions showed but a minimum of starch and this 

 is located in the cells of the cortex. In short, where large slices 

 of the healthy and diseased tissue were laid in weak iodine in a 

 porcelain dish the former showed little or no starch, while the dis- 



eased portions appeared almost black. 



Thin sections of the large tubercles formed by Rhizobium 



