A Disease of Tomatoes. 
21 
Mycosphcerella citrullina, Grossenbacher. This fungus causes a 
serious disease of melons in the United States, the pycnidial stage 
there being followed by the formation of perithecia which, however, 
do not develop until the tissues are dead or dying. We cannot 
find any record of the perithecial stage having been found in this 
country, and in the course of our own work perithecia were not 
seen, although plants and fruits killed by the fungus were kept in 
an exposed situation during the winter in order to try to induce 
their formation. 
General Remarks. 
As with so many other pathogenic fungi little is yet known of 
the manner in which infection by this fungus occurs in nature. 
The facilities which might enable such a matter to be solved have 
not been available to us. Such problems can be best studied in 
tomato houses and gardens developed on practical lines, although 
used primarily for experimental purposes. At present we do not 
know of any place in England where such work can be pursued in 
an adequate manner. 
In one plot of out-door tomato plants in Cambridgeshire the 
disease occurred two years in succession, and in view of the apparent 
absence of a perithecial stage in this country and of the fact that 
the tomato plant is an annual, it is not clear how the disease is 
propagated from one year to another. It is possible that the 
mycelium hibernates in the dead tissues of affected plants, and it 
may be that portions of diseased plants left on the ground instead 
of being burnt are the means of reinfection if plants are set out on 
the same plot the following year. There is no evidence yet that 
the fungus is propagated in the seed. On out-door plants the 
disease does not appear to develop until almost fully grown. In 
the plots referred to above only 3 per cent, of the plants were 
affected and the distribution of diseased plants was sporadic, so 
that the disease is not likely to become a serious pest to growers 
of out-door tomatoes. In the case of tomatoes grown under glass, 
Massee 1 has already pointed out how severe an epidemic this 
fungus may cause on account of the conditions of growth being so 
favourable for its development. In consequence of its virulence 
under these conditions it is included in the list of pests scheduled 
by the Board of Agriculture, under the Destructive Insects and 
Pests Acts. 
1 Massee, G. Kew Bulletin, 1909. 
