MOSAIC DISEASES 143 
exist, and may be found singly on individual plants or 
together on the same plant. The first type consists of 
a simple mottling of the foliage without distortion of any 
kind. Pale green areas appear between the veins, and 
in process of time these turn yellow, with an indistinct 
margin. ‘The second type resembles the first somewhat, 
but the spots produced appear very quickly without any 
gradual transition from pale green, and are distinct in 
outline and deep yellow in colour, like the variegations of 
Aucuba Japonica. This type is probably similar to the 
aucuba-mosaic of the potato described by Quanjer (39). 
The third type shows a distorted leaf margin, but without 
blistering or mottling. 
In the fourth type blisters are produced on the leaf 
surface, and the leaf margin is more or less distorted. 
There is no mottling (Fig. 39). The fifth type, or tendril 
type, is distinguished by a reduction of the lamina and the 
production of fern-like or tendril-like leaves. Mottling is 
absent. 
While a considerable amount of investigation is 
necessary before the full facts are available, it would 
appear that these symptoms are manifestations of the 
same disease, their appearance being governed by a 
number of factors, chief of which are the environmental 
conditions under which the host plant is grown and the 
degree of resistance exhibited by it. Thus, most varieties 
of tomato plants inoculated in February and March 
develop distorted, blistered leaves without mottling, but 
as the season advances these symptoms are gradually 
replaced by mottling and distortion. Towards the end 
of the year the new leaves develop blisters and become 
distorted, but mottling is rare. 
The type of symptom exhibited by the host may 
vary with the variety, even when the conditions are 
uniform. Thus in the case of Manx Marvel and In- 
vincible mottling of the foliage occurs later in the year 
than it does in the case of other varieties like Kondine 
Red, Blaby, and Comet. The flowers of tomato plants 
