THE CONTROL OF PLANT DISEASES DUE TO FUNGI. 21 
on the one hand and on the other from the ' Crimson Rambler,' derived 
from Rosa multiflora Thunb., a bad mildewer, introduced originally 
from Japan. A number of varieties known or suspected to be of 
' Crimson Rambler ' parentage are highly susceptible to mildew, such 
as ' Purple East 'and ' The Lion,' derived from 'Crimson Rambler' 
and ' Beaute* Inconstante ' j and ' Leuchtstern ' and ' Flower of Fair- 
field/ in which ' Crimson Rambler ' blood is suspected. There is, 
on the other hand, an important class of Roses having as a parent 
R. Wichuraiana, an immune Japanese single Rose and possessing a 
higher degree of immunity than the R. multiflora derivatives. Can 
we not aim then at obtaining all the characters we value in the multi- 
flora group from the less susceptible Wichuraianas ? Again, the 
Hybrid Perpetuals, derived largely from the susceptible Damask 
and Gallica Roses, are paralleled by a relatively less susceptible 
series — the Hybrid Teas — descended from forms exhibiting strong 
likeness to the more immune China Roses. Can we not raise from 
Hybrid Tea parentage forms equal to the finest among Hybrid 
Perpetuals ? 
Some of the difficulties * to be met with in the attainment of our 
ideal may be gathered from the case of Peaches and Nectarines. 
Here the question of immunity from disease is exceedingly complicated, 
not only because we cannot yet distinguish all the symptoms due to 
Exoascus deformans from other troubles to which these trees are 
liable, but Exoascus itself varies in virulence to a remarkable extent 
according to weather, soil, and cultural conditions. It is not so easy 
to distinguish such distinct types as exemplified by the multiflora 
and Wichuraiana Roses. Some varieties appear to attain an almost 
cosmopolitan susceptibility, such as, for example, the variety ' Elberta,' 
which is recorded susceptible for the United States, Britain, and 
Australia, although, curiously enough, the variety ' Kia-Ora,' a seedling 
raised from ' Elberta ' (on a Peach stock) in New South Wales, is 
recorded as free from disease. For other varieties the record varies ; 
thus * Briggs' Red May ' is resistant in Australia, susceptible in the 
United States and Tiflis. A short time ago, by the courtesy of the 
Imperial Bureau of Entomology, I received some valuable information 
from Professor Jachewsky on the subject of varieties immune to 
Exoascus in Asiatic Russia. Professor Jachewsky writes that the 
' Early Alexander ' and the American varieties, such as ' Amsden ' 
(susceptible at Tiflis), are recorded immune by Band art jev for the 
Black Sea district, where Exoascus is a veritable scourge J the variety 
' Markwallia gauri ' is recorded immune in the government of Kutais 
by Kwaratschcha ; the varieties ' Daghestan ' and ' Queen of the 
Gardens ' were noticed to be immune by Nemadowski inlhe botanical 
garden of Tiflis, whilst the European varieties obtained from seeds 
are reported immune in Kachetia, where the local species are badiy 
attacked. 
* See also difficulties of another kind experienced in the case of the sugar- 
cane described by Barber in Ann. Appl. Biol. i. Jan. 1915. 
