July 14,19*3 
Degeneration Diseases of Irish Potatoes 
53 
peared in the inoculated hills and where even the progeny of diseased 
hills showed no symptoms during the summer (p. 49). The eight con¬ 
trols and 13 of their progeny grown in the greenhouse were healthy. 
A number of leaf-mutilation inoculations with rugose mosaic were per¬ 
formed again in 1922, usually with current-season symptoms in the open 
field as well as in the cages (p. 76). 
Intervarietal aphid transmission of rugose mosaic to Green Mountains 
will be described later (PI. 4, A). 
streak 
Most of the streaking seen by the writers has been associated with 
rugose mosaic (PI. 4, B, C), but in at least one case the latter was absent 
so that streak (5, p. 50; 33; 29, p. 76-82; 4) may be considered as a distinct 
symptom complex. The current-season symptoms appear in a certain 
order after leaf-mutilation inoculation, as streaking and spotting, burning, 
brittleness, leaf dropping, and premature death, with no mottling except 
for chlorotic spots a few hours previously in the places where streaking 
and spotting occur, and no wrinkling (PI. 5, A, C; 11, C; 12,B). 
Symptoms following tuber perpetuation are extreme dwarfing, wrink¬ 
ling, curling, rugosity, brittleness, leaf dropping, and premature death 
(PI. 6, A, 2, B, 1). In this connection a study of other works {29, p. 80; 
4, p . 16) is interesting. The tuber symptoms are extreme reduction in 
size, with some darkening, near the eyes, that resembles small initial 
infection spots of late blight; Phytopthora infestans de By. Cracking 
or splitting of the tubers has been observed for streak by Atanasoff 
(4, p. 9), as also for curly dwarf and leaf roll by Orton ( 32 , PL 13), for 
yellow dwarf by Barrus and Chupp (7), and for unmottled curly dwarf 
by the writers (p. 60). 
Intervarietal transmission was effected in 1921 (p. 69; PI. 5, A, C) as 
previously reported (42). These results were confirmed with the same 
methods of inoculation within the Green Mountain variety in 1922, 
described later. In regard to the 1921 report, Atanasoff (4, p . 18-19) 
writes: 
b. Plant juice. Schulz and Folsom claim to have been able to infect potato plants 
with stipple-streak by means of juice from an infected plant. “ In 1921, *' they write, 
'‘juice from a streak plant applied to 20 mutilated Green Mountain and Irish Cobbler 
plants caused infection in 19, with typical symptoms appearing in some in 12 days. 
He then describes inoculations made in Holland “in order to verify 
this statement” and concludes it to be “highly improbable that the 
plants infected by Schulz and Folsom have become diseased as result of 
their infection. ” Some discussion seems necessary here. 
The above quotation (42) should have been completed as follows: 
Sixty control hills in the same tuber units, from quartered tubers, remained healthy. 
The following of inoculation by the disease in 95 per cent of the 20 
inoculated hills, in two varieties, with the absence of both inoculation 
and disease in the 60 control hills, is a contrast more convincing, at 
least to the writers, than reports of successful grafting with all figures 
omitted (4, p. 20), though the writers by no means doubt the latter report. 
It is a contrast less impressive than with 100 per cent, or with 95 per 
cent in 2,000 inoculated hills, but is nevertheless significant. 
