DISEASES DUE TO FUNGI 103 
with sulphur at regular intervals by means of a mechanical 
vaporizer and to provide efficient ventilation. 
Leaf Spot Disease of the Tomato.—This disease, due 
to Septoria lycopersict Speg., is described as being a 
serious one in America, but fortunately it has not yet 
appeared in this country. It can easily be recognized 
by the appearance of numerous spots with light grey 
centres and dark margins. Levin (28), who carried out 
a careful investigation of this disease, describes the 
symptoms as follows: 
“The earliest indication of the disease is a water- 
soaked spot which can be distinguished with a hand lens 
on the underside of the leaf. There is no noticeable 
discoloration of the tissue at the outset. As the spot 
grows larger it becomes more or less circular in outline 
and shows a definite margin. The affected tissue darkens, 
becomes shrunken, and later appears hard and dry. The 
colour of this spot may vary from black to greyish-white. 
The spots may vary in shape and size from a small 
circular spot of pin-head size to a large irregular spot of 
about 2 cm. in diameter. Not infrequently the spots 
coalesce. While the tissue is shrinking three to ten 
small, black, glistening pycnidia appear in the spot. 
Finally, yellowish mucilaginous masses can be seen 
exuding from the pycnidia. Upon microscopic examina- 
tion these are found to be masses of long, filiform spores. 
The number of pycnidia are well defined, visible with the 
naked eye, and separate. Pycnidia may occur on the 
underside of the leaf; usually, however, they occur on 
the upper side. At this point it must be noted that not 
all spots contain pycnidia when the leaf dies. This point 
will be taken up in detail later. 
“* About the time of spore exudation the green tissue 
of the leaflet contiguous to the fungous spot begins to 
turn yellow. This yellowing increases, eventually in- 
volving the entire leaflet. ‘Then the fungous spots which 
have been so far pliable become dry and brittle. The 
