20 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
of Rose mildew in a collection may be due to the presence of infective 
briars in a neighbouring hedge ; it may also be introduced by the 
use of susceptible briar stocks ; in such cases suckers * which appear 
early in the season and are not removed may become mildewed and 
provide the fungus with a first hold in the garden, f Black spot of 
Roses, which is frequently stated to have been introduced on the 
Austrian briars, also occurs on our hedge Roses, and I have also found 
it on certain stocks at present in commerce. These evils may be 
ameliorated to a certain extent by careful choice of sites for a rosary 
where there is any latitude for choice, by judicious grouping of varieties, 
and by selecting disease-free and if possible immune stocks for grafting 
purposes. 
Some pests are difficult to control from their habit of passing 
phases of existence in more than one host. I will give as an example 
a case sent to Wisley for diagnosis last year that will prove of excep- 
tional interest, for the self-same disease was under discussion before 
this Society just over a century ago. The fungus concerned, which 
belongs to the rusts, was known in those days as Lycoperdon can- 
cellatum, and was recorded from Downton and localities in the vicinity 
of London by Thomas Andrew Knight as destroying the leaves and 
branches of the Pear tree. Pear leaves with this Lycoperdon, now 
styled Gymnosporangium, which bore the pycnidia of one species — 
G. Sabinae, (fig. 3)- — and leaves of the Quince from the same source 
were infected with the aecidia of a second and rarer species- — 
G. confusum (fig. 4). Both fungi pass the winter on the Juniper, and 
the Pear and Quince are liable to re-infection each season from this 
tree. 
Within the last decade we have been led to hope, especially from 
the brilliant work of Biffin, that our destiny with regard to the 
control of fungal disease rests with the breeders of new forms of 
plants, for much has been accomplished towards raising disease- 
resistant races of our most valued economic species of wheat, cotton, 
sugar, &c. It is an effort that should spread far, and it could not 
obtain happier application than when designed to produce immune 
or semi-immune races of plants resistant to the annual visitation of 
mildew. Considering Roses, we should picture a Utopian landscape 
where the flowers retain the properties we cherish — those subtle 
perfumes, those blended colours of sunset or sunrise, their exquisite 
form — invested with the mantle of immunity j for even though we 
may not enter the promised garden the foundations may be laid of 
future creations leading to successes that will excel the hard-won 
triumphs of to-day. 
Now, mildew in Roses is of multiple origin. Undoubtedly two 
sources of influx and spread are through the Hybrid Perpetual Roses 
* This actually occurred in a garden in Surrey in 191 5 ; the mildew appeared 
on a sucker from a standard stock in April. 
f With regard to Roses under glass, there seems no insuperable difficulty in 
keeping them free if we could start with a mildew-free house. 
