40 BULLETIN" 64, U. S. DEPABTMENT OF AGKICULTUBE. 
This is a problem in varietal decline that should receive earnest con- 
sideration. The prevalence of such weak plants should be ascer- 
tained in any stock intended for propagation, and measures undertaken 
to provide disease-free seed potatoes in sufficient quantity to meet 
all demands. 
There are all grades of the condition above described, from pro- 
nounced types of curly-dwarf to those approaching normal vigor. It 
will furthermore be apparent that this is a difference inherent in the 
varieties or strains under observation. Schander has described a 
related condition as the "Barbarossa disease," so named because 
it is characteristic of the German variety Barbarossa, In every 
potato field are found some weaklings, or plants which are merely 
small, without any curled leaves or dwarfed stems, and without the 
fungous lesions described under " Rosette." The extent to which these 
small plants represent a permanent deterioration in the vigor of the 
stock, and thus a condition related to the curly-dwarf, is a problem 
not yet settled. Certainly such weaklings should be eliminated when 
improved seed is desired. 
CONTROL OF CURLY-DWARF. 
Since potatoes from diseased hills can not be restored to vigor, all 
such should be rejected for planting. The occurrence of any consider- 
able number in a field may be taken as evidence of a general decline, 
requiring that the entire stock be given up and new seed substituted. 
It has already been demonstrated by Prof. Stuart that we have in 
the method of tuber selection outlined by Webber (1908) a means 
by which all diseased potatoes may be eliminated from a stock, 
since when all tubers are cut into four pieces and these planted in 
adjacent hills all those which show inherited weakness may be 
eliminated and only the strongest and most productive selected. 
ROSETTE. 
Phases of leaf-roll and curly-dwarf marked by dwarfed growth 
and the formation of aerial tubers have been described. These symp- 
toms may, however, result from another cause — the stem lesions 
due to Rhizoctonia, and no attempt to differentiate potato troubles 
can be successful which does not take into consideration the varied 
effects of this fungus. It must be recognized that Rhizoctonia appears 
to be a more active parasite in America than in Europe and to play a 
greater role in the Western States than in the Eastern. 
Since this article is written primarily to effect a diagnosis of 
potato troubles, it will not be necessary to review the facts already 
well known to pathologists relative to the occurrence of Rhizoctonia 
on its various hosts or to discuss the relationship and parasitism of 
the several known strains. This subject is being fully reinvestigated 
