Mar. 17. 1919 Fusarium-B light of Potatoes under Irrigation 285 



region, is the weakest and least protected. There is a difference in the 

 susceptibility of seed of different varieties, but what seems more im- 

 portant is that seed of the same variety from different sources varies 

 greatly in its power of resistance. The rot following infection may be 

 swift, and the fungus will destroy the seed piece before germination 

 begins. 



Plate 37, E, illustrates a seed piece upon which no eye has germinated, 

 though the piece is nearly destroyed by rot. In this illustration two dark 

 spots are to be noted in the vascular region, denoting vascular infection; 

 'yet no decay originated at that point. When the decay is slower, the 

 seed germinates and sends up a vigorous shoot. Plates 37, D, and 38, D, 

 illustrate cases of germination followed by seed-piece rot. The region 

 adjacent to the active tissue is the last to decay because it is more resistant 

 and because the decay begins in the loose parenchyma and advances 

 toward the germinating point or place of attachment of the shoot. Where 

 decay is delayed sufficiently to allow germination to take place, the decay 

 works slowly through the active region, or it may stop temporarily. 

 Plate 37, D, illustrates how the decay is delayed nearest the growing part 

 and how it advances evenly toward this region. Plate 39, D, illustrates 

 the base of a plant the seed piece of which had decayed thoroughly. The 

 stem is cut away, showing the healthy tissue within and the absence of the 

 parasite. The general good health of the roots should also be noted. 



Some plants appear to grow normally for a few weeks, after which 

 symptoms of disease begin to appear. The color may or may not "change, 

 and the leaves may show curling, rolling, or wilting. One lower leaf may 

 turn yellow, wilt, and fall, while the remainder of the plant is a picture of 

 health. In a single hill containing two or more sprouts the tip of one 

 may wilt and the other remain healthy. Plate 40, C, represents a plant 

 consisting of two stems, one of which is healthy, the other wilting. The 

 stem at the left will die, while the stem at the right may live through the 

 season and >neld normally. Upon taking up such a plant the decay of the 

 seed piece will be shown to have advanced toward and into the wilted 

 stem, while in all cases the root system is healthy in every branch. 

 Plate 40, B, shows the top of a plant consisting of three stems. The top 

 leaf and the one below it on the same stem are wilted. Neither the other 

 leaves nor the color of the plant indicated anything abnormal. Plate 

 39, C, shows the seed piece and the three stems of the tops illustrated in 

 Plate 40, B. The wilted leaf shown in Plate 40, B, is on the middle stem 

 pictured in Plate 39, C, which is at the center of the decay. The stem at 

 the left, healthy on Plate 40, B, is here shown with a slight sound area 

 remaining in the seed piece. A stem which shows these symptoms in 

 early summer when conditions are favorable may not at once succumb, 

 but is usually doomed to an early death. Plate 39, B, shows a young 

 plant in which the decay advanced continuously from the seed piece into 



