22 



BULLETIN 64, U. S. DEPARTMENT OF AGEICULTUEE. 



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. 



No. 



10 

 11 

 12 

 13 

 14 

 15 

 16 

 17 

 18 



Trial ground. 



Double 

 cent- 

 ners. 



No. 



Trial ground. 



Double 

 cent- 

 ners. 



1 





407.8 

 258.2 

 245.6 

 228.7 

 213.3 

 212.8 

 197.6 

 192.0 

 187.2 



Hadmersleben 



Scharrau 



Marienfelde . . . 



187.2 

 182.6 

 181.0 

 180.8 

 176.2 

 164.4 

 154.8 

 151.2 

 150.0 



19 



20 

 21 

 22 

 23 

 24 

 25 

 26 

 ■27 



Loehme 



140.0 



2 



Greisitz 



Calvoerde 



Erbesbuedesheim. . 



Gross-Saalau 



Hohenlieim 



Singlingen 



131.8 

 130.0 



4 



Klein-Raudchen 



Dahlem 



Freistatt 



Altneuhaus 



Koetzig 



Neudorf 



Klein-Spiegel 



Schaeferhof 



129.6 

 128.0 



6 



Siegersleben 



Mittlau 



Dolgen 



128. 2 





Neckarau . 



128.0 



S 



Althoefchen 



Gieshuegel . 



98.0 



q 





Altkluecken 



78.2 









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 hrowning 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 Verticillium albo-atrum is present. When leaf- 

 roll first appeared Appel commented on its strikmg 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 seen 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 brownmg 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 



