22 
BULLETIN 64, U. S. DEPARTMENT OF AGRICULTURE. 
gave in Groebzig a yield of 274 bushels per acre. The next year, however, the yield 
decreased so much (the exact record is not known) that the breeder, Gen. Oekonomierat 
Sauberlich, discarded it as unworthy of cultivation. To what extent such varieties 
not too badly diseased have their yield influenced by external conditions is shown by 
a comparison of the yields of this sort on the different trial grounds of the German 
Potato-Culture Station, which in the year 1907 were planted with the same seed from 
Holland . There were harvested in double centners per hectare : 
No. 
Trial ground. 
Double 
cent- 
ners. 
1 
, Double 
No. Trial ground. cent- 
j ners. 
No. 
Double 
Trial ground. j cent- 
: ners. 
[ 
1 
Groebzig 
407.8 
258.2 
245.6 
22S.7 
213.3 
212.8 
197.6 
192.0 
187.2 
: 10 Hadmersleben 
11 1 Scharrau 
187.2 
182.6 
181.0 
ISO. 8 
176.2 
164.4 
19 
20 
21 
22 
23 
24 
25 
26 
27 
Loehme 140. 
? 
3 
Calvoerde 
12 J Marienfelde 
Gross-Saalau 130. 
4 
Klein-Raudchen 
Dahlem 
Freistatt 
13 j Klein-Spiegel 
1 14 Schaeferliof 
Hobenheim ! 129. 6 
Singlingen j 128. 
Dolgen 128. 2 
fi 
1 15 Siegersleben 
7 
16 Mittlau 
154.8 
Neckarau . . . 128. 
8 
1 17 Althoefchen \ 151.2 
18 ' Ostrowitt ! 150.0. 
Giesbuegel. . 98.0 
9 
Neudorf 
Altkluecken 78. 2 
I 
Of the destructive effect of leaf -roll on the potato yield, this country 
has altogether too good an example in the outbreak of 1911 and 1912 
in Colorado. (See p. 31.) 
Stem-end browning of tubers is no longer considered a reliable evi- 
dence of leaf-roll, nor is there any other character by which the 
disease may be detected through an inspection of the tubers. In 
European potatoes more or less discoloration of the vascular tissue 
is frequently to be found near the stem end, though this is never so 
conspicuous, according to the writer's observation, as the familiar 
stem-end browning associated with Fusarium wilt in the United 
States, except when VerticiUium albo-atrum is present. When leaf- 
roll first appeared Appel commented on its striking similarity to the 
Fusarium wilt described by Smith and Swingle (1904) and wrote of 
the German disease: 
If one cuts through the stem ends of diseased tubers, one finds that the vessels for 
one-half to 1 centimeter under the skin have a yellow discoloration. This discolor- 
ation is at harvest time to be 6een more clearly near the stem end, but later extends 
until in spring it can often be traced into the eyes. Generally such tubers are less rich 
in starch than the healthy ones. 
This discoloration was then thought to be characteristic of leaf-roll 
and evidence of the causal connection of a Fusarium with it. More 
extended observations threw doubt on this point, and it is now gen- 
erally agreed that stem-end browning of the tubers is not an insep- 
arable feature of the leaf-roll. Appel and Schlumberger (1911) say: 
The discoloration of the vascular bundles was at first understood to be a character- 
istic of the leaf-roll,, as announced by Appel on the basis of conditions observed in 
1905 and 1906. This discoloration should consist in a partial browning of the bundles 
of the stem and in a yellow color of the tuber bundles, which in mild cases confines 
itself to the vicinity of the stem end but in severer cases extends through the entire 
vascular ring. Later, however, in the year 1907, when the potatoes almost everywhere 
