142 DISEASES OF GLASSHOUSE PLANTS 
Distortion.-—The effect of the disease upon leaf growth 
also shows itself by a reduction in size of the leaf blade, 
with a consequent alteration in the position of the veins, 
and the assumption by the edge of the leaf of a fantastic 
form. This is especially noticeable in the case of the 
tomato, where filiform and fern-like leaves are common. 
Among growers, plants affected in this way are said to 
be suffering from “‘ sweet-pea disease,” because the leaf 
blades are often reduced to such an extent that only 
the mid-ribs remain, and the resemblance to sweet-pea 
tendrils is obvious. 
Similar effects have been noticed in the case of the 
petunia and tobacco. Distortion of the symmetry of 
the leaf is a common symptom, produced by retarded 
growth at certain parts of the margin. In some cases 
as many as 43 per cent of the tomato flowers have been 
observed to fall from diseased plants, the fall from healthy 
plants under the same conditions being 2 per cent. 
In other cases abnormal fruits have been observed, and 
a considerable reduction in the number of viable seeds 
in each fruit. 
Other symptoms connected with mosaic disease in 
general are a dwarfing of the plants and a general paling 
of the foliage. Many investigators have examined the 
roots of diseased plants, but have been unable to 
determine any definite root symptoms. 
Symptoms of Tomato Mosaic Disease 
The appearance of tomato plants infected with mosaic 
disease varies considerably, according to infection having 
taken place in the early or late stages. Plants infected 
when quite young develop typical symptoms in all parts. 
They are generally stunted in growth and paler in colour 
than normal plants. Those infected later in life show 
typical symptoms only on those parts which develop 
after infection. 
In respect of the foliage, five main types of symptoms 
