90 



PROTECTION OF PLANTS, 1921-22 



Frequently, however, the skin is more or less cracked and rassetted and a still 

 more advanced stage may give rise to scabbing. In this condition drying out in 



storage or the entry of secondary 

 organisms is facilitated. 



If the soil is wet or poorly 

 drained and the temperature high, 

 severe infection may completely 

 cut ofT the young shoots before 

 they appear above ground and 

 this in some measure accounts for 

 misses in the field. Sometimes side 

 branches may grow up from below 

 the lesion on dead haulnis (Fig. 

 12) but sach branches are weak 

 and spindling, with yellowish 

 leaves. Older plants severely at- 

 tacked just below^ ground wilt and 

 die off rapidly. Slight attacks 

 will produce lesions on the stem 

 tending to girdle it and in this 

 case the tops are more or less 

 dwarfed and j'^ellowed. As the fun- 

 gus graduallj^ encircles the stem 

 and penetrates the tissues, water 

 supply is cut off increasingly so 

 that there is a shortening of 

 upper internodes and dwarfing of 

 leaves which gives rise to ''rosette 

 top". At the same time the leav- 

 es may be slightly wulted and 

 yellowish to reddish green in color 

 and curled. This curling is easily 

 distinguished from the crisp con- 

 dition in true Leafroll. 



When the stem is attacked at 

 the time of early tuber formation 

 so that ample food is being ela- 

 borated, the girdling of the stem cuts off the translocation of food to the 

 stolons. This disturbance in direction of translocation causes the develop- 

 ment of aerial tubers in the axils of leaves. I found man}^ such cases in 

 France during the war and in all cases where aerial tubers were formed there 

 was a closely matted weft of mycelial growth around the stem for about two 

 and a half inches above groimd level. That the formation of aerial tubers is 

 not due to root injury, but changed translocation of elaborated food, can be 



Fig. 10— Dry .stem-rot of potato. Xotethat le- 

 sions occur about at ground \e\e\ and that the 

 plant may branch out again from bek w. (.After 

 Bull. 85." Mich.) 



