188 NATURAL SCIENCE. March, 



evident until about the end of June, when the stem or bine has grown 

 some distance up the pole. Then the bine becomes slack, and loses 

 its power of twining. The head of the plant hangs away from the 

 pole, and if the plant is not retied at a higher point the whole mass of 

 stem and leaves slides down into a heap on the ground. When this 

 stage is reached, further growth and development are arrested, the 

 plant becomes worthless, and is generally grubbed. Those specimens 

 which show symptoms of disease one year are almost invariably worse 

 the following summer. What the ultimate result is I have not been 

 able to learn from direct observation, but I am informed that the plant 

 dies away altogether. 



Stages between apparent health and complete ruin are always to 

 be met with. It is not infrequent to observe some bines diseased, 

 which are nevertheless sufficiently strong to reach the top of the pole, 

 and even to yield a moderate quantity of hops ; but by far the larger 

 number in an infected garden are overcome before reaching this stage. 

 Upon the same " hill " it may often be noticed that some bines topple 

 over, and others remain normal. The diseased and normal stems in 

 such instances generally grow from different " sets," and the cures 

 said to have been produced by cutting off the affected bines and tying 

 up others may be explained by a consideration of this fact. In one 

 or two cases, however, I have noticed two bines springing from 

 opposite sides of the same root stock, one of which showed symptoms 

 of disease, and the other an apparently healthy growth. 



In a diseased plant the stem not only loses its twining power but 

 tapers rapidly, becoming very thin ; the branches and young shoots 

 also have the same extremely thin character, and the internodes of 

 the plant are shortened, so that the leaves become more crowded than 

 in healthy bines. The growth in length of the fibro-vascular system, 

 or woody parts, all through the plant seems to be arrested. 



The most characteristic symptom of the disease is the peculiar 

 leaf development. The earlier leaves differ little from the ordinary 

 type, and die a natural death. Those formed later are, however, very 

 much smaller than usual, often darker in colour, and their edges curl 

 towards the upper surface. (Plate III., Fig. I., b). The " veins " on 

 the under surface stand out from the soft tissue in a marked degree 

 (Plate III., Fig. I., a), and this, together with a slight puckering and 

 increased serration of the leaf, makes it closely resemble the leaf of the 

 stinging-nettle. On holding a leaf up to the light and viewing the 

 under-side, the chief veins are seen to be drawn together at the angles 

 where they branch from one another, and between them at these points 

 are noticed yellowish transparent patches of thinner tissue. These 

 patches are surrounded by thicker dark-green tissue, which also 

 extends along the sides of the veins for a short distance. These are 

 the first indications of the disease, and arise generally at the edges 

 of the leaf and then extend backward along the sides of the veins to 

 the middle and even to the base of the leaf-blade. Before curling 



