THE CONTROL OF PLANT DISEASES DUE TO FUNGI. 19 
sites for incipient canker that will ultimately involve the death 
of the branch, if not that of the whole tree. 
The appearance of disease of some kind or other being almost 
inevitable under present conditions, however careful the cultivator, it 
is important to record the presence of a malady the instant it appears 
in a nursery or house. Quite recently I was able to bring to the 
notice of the Scientific Committee * a case of the introduction of 
black spot into a garden on the ' Lyon ' Rose, where neglect to deal 
with the trouble at once led to its appearance on more than a dozen 
varieties in the second season. An outbreak of Carnation rust was 
averted at Wisley in 1915 by removing an infected plant which had 
been recently added to the collection from the Carnation house and 
placing it in quarantine. After suitable treatment the plant and six 
cuttings taken from it were restored to the house and proved 
absolutely rust-free. Both rust and black spot are caused by parasitic 
fungi, and needless to say much trouble would have been saved if 
they had not been introduced. The greater the precaution taken on the 
part of the consignor and consignee the less the chances of undesirable 
intrusions of this kind. One of the chief difficulties lies in the lack 
of trained observers to detect fungal pests in their different forms 
at an early enough time. Action is almost universally delayed until 
the symptoms are plainly manifest. In the case of the American 
Gooseberry mildew, an outbreak was detected at Wisley by a trained 
observer within a few days of the initial infection, but imperfectly 
trained observers did not detect the outbreak for at least another 
week after the first observation. Now the control of the whole 
epidemic might depend on the treatment of the mildew within this 
single week. 
An outbreak of disease in a garden is of course not necessarily due 
to the actual introduction of a pest in imported plants. The germs 
of disease may lurk among samples of seed — in this way the winter 
fruits of the Delphinium mildew f may be distributed if the seed be 
collected from mildewed plants and sent out contaminated' — in packing 
material, sacking, boxes, straw, &c, wherever the winter or resting 
forms of fungi (sclerotia, sclerotial mycelium, resistant spores, &c.) can 
remain concealed. Cases and receptacles used for collecting apples, 
pears, &c, would be especially liable, and soil from infected areas 
containing the spores of Plasmodiophora, the spore-balls of Spongo- 
spora, or the sporangia of Chrysophlyctis. Special attention to 
cleanliness will meet these cases — clean stock, clean handling, and 
clean packing. 
A source of disease frequently overlooked is the infection of a 
cultivated variety from its wild congener. A notable example is the 
occurrence of finger-and-toe in common hedge crucifers. The incidence 
* See " Proc. Sci. Com. Roy. Hort. Soc." in Jour. Roy. Hort. Soc. xli. p. cxcviii. 
t The winter fruits (perithecia) are frequently formed in very large quantities 
on the stems, leaves, flowers, and fruit of susceptible varieties, and it is difficult 
to collect the seed without obtaining the small black perithecia as well unless 
special precautions are taken. 
. c 2 
