83 
tissues of diseased asters. The writer,* however, has 
proved that a species of Phytophthora is the primary cause 
of the Black-Leg disease and that Fusarium only appears 
later as a saprophyte living upon tissues previously killed 
by the other fungus. The Phytophthora is always present 
in the diseased asters even in the earliest stages; it has 
been isolated and grown separately from all other organ- 
isms, and the disease has been produced artificially from 
such growths. Other organisms found on diseased asters, 
including Fusarium, are unable to infect and produce wilt- 
ing in healthy plants; such saprophytes only succeed after 
the tissues have been killed by the Phytophthora. 
The insidious nature of this disease renders it extremely 
difficult to deal with, for it is usually almost impossible 
to detect diseased plants until the wilting actually sets in. 
Whilst sufficient scientific trials of remedial measures have 
not yet been made to warrant promise of complete success 
in all cases still some precautions may be indicated. 
The soil of the seed-bed should be partially sterilised 
by steam or hot water and asters should not be planted in 
ground which produced diseased plants the previous sea- 
son. All diseased material should be removed and 
burned and the infested soil thoroughly drenched with 
Formalin (1 pint per to galls. water) and covered with 
sacking for a few days. Many growers raise aster seed- 
lings on hot-beds of stable manure, but these conditions 
should be avoided since they are much more favourable 
to the fungus than when alkaline artificial manures are 
used. 
As a first example of the common diseases of leaves, 
the Tomato-leaf rust or mould caused by Cladosporium 
fuluum may next be considered. This is more strictly a 
disease of the leaves than is the Late-Blight of potato, 
but even in this case the whole tomato plant suffers 
because of the attack on the leaves. The disease, which 
has been known in this country for over a quarter of a 
century, first appears on the leaves in the form of small, 
yellowish spots. These gradually increase in size and 
often run together, and the under surface of the leaf 
in the diseased areas becomes covered with a rusty, velvety 
growth. This is the reproductive part of the fungus pro- 
** Annals of Applied Biology.” Vol. II., Nos. 2 and 3, July, 
IQ15, DP. 125-137. 
