July 14, 1923 
Degeneration Diseases of Irish Potatoes 
ill 
uncaged Bliss Triumph stock of the same original strain as the caged 
plants grown in the same locality increased from 15 to 84 per cent mosaic. 
Similar observations were made by Krantz and Bisby {21, p . 18-19). 
That the protective effect of caging is due to insect exclusion rather 
than to its modification of climatic factors is shown by the many cases 
described previously of infection within cages by introducing virulent 
insects. 
In this connection it is interesting to note that Murphy ( 31 ) finds that 
capsid bugs and jassids transmit leaf roll of potato in Ireland, where those 
insects apparently are more important in this respect than aphids. 
Elmer (1 3) reports successful cross inoculations by transferring mealy 
bugs (Dactylopus sp.) from mosaic infected Solanum and cucurbit plants 
to healthy cowpea (Vigna catjang) seedlings. Such observations confirm 
the general assumption that possibly a number of different insects may 
be found which transmit these diseases. 
GENERAL CONCLUSIONS 
In addition to a subsequent summary including the various facts 
demonstrated in this paper, two general conclusions may be pointed out, 
relating, respectively, to the r 61 e of diseases in the degeneration of pota¬ 
toes and to the general influence of region on the degeneration-disease 
problem. 
“Running-out” is generally recognized as relating to plants which for 
various reasons fail in the maximum production. Unfavorable soil and 
weather conditions, senility, reversion, and loss of vigor due to prolonged 
asexual reproduction are some of the causes to which degeneration in 
plants has been ascribed. While such factors as favorable soil and 
climate undoubtedly play a very effective r 61 e In the proper develop¬ 
ment of plants, it must also be recognized from the comparatively 
recent investigations on degeneration diseases in plants that no matter 
how favorable the conditions for development, a diseased plant will be 
less productive than a healthy one of the same species and variety in the 
same environment. 
Perhaps in no other plant has the theory of senescence been so fre¬ 
quently mentioned as with the so-called degeneration or deterioration 
of the potato. Abnormalities due to mosaic, leaf roll, and spindling tuber 
heretofore have frequently been ascribed to the asexual reproduction of 
the potato. In view of the recent findings regarding the nature and 
infectiousness of these maladies, it is no longer necessary to mention 
senility in connection with them, as pointed out by Cotton (jo, p. 163 - 
164 ). When one realizes that a large percentage of healthy plants exists 
in many of the potato varieties propagated asexually for many years, one 
questions rather seriously whether senescence plays any r 61 e whatsoever. 
In this connection, as Cotton (10, p. 164) has pointed out, many of 
our most persistent weeds continue to reproduce very successfully almost 
entirely through asexual reproduction. 
The evidence on the presence and importance of degeneration diseases 
of the potato also shows that a knowledge of the pathological significance 
of an abnormal condition of a plant is as necessary as a knowledge of 
its cultural or genetic relations, if reliable deductions are to be drawn 
(jo, p. 164). 
Furthermore, it is apparent that these degeneration diseases must be 
recognized in any authentic comparison of strains of potatoes in the 
