16 G. MASSEE PAEASITIC FtTNGT. 



rose-growers have been troubled by finding the leaves and flo"wers 

 of their rose-trees covered with mildew of a greyish white colour, 

 which begins to show itself in the budding stage of the plant, 

 grows with it through the year, and in the end destroys it. The 

 name of this fungus is Sphcerotheca pannosa. It is called pannosa 

 because it forms a felt-like film of mycelium on the plant. It 

 travels all over a leaf, and, when it has collected a sufficient amount 

 of nutriment from the substance of the leaf, it creeps off and spreads 

 over other leaves, after a time falling off in a fine jiowder. This 

 is what is commonly known as mildew, and in all cases of mildew 

 the course of the disease is the same and the mode of attack is the 

 same. The great object which the fungus has in view is rapid 

 distribution. It is blown about by the wind, and any of it in this 

 state of fine powder which alights on the leaves of rose-trees 

 germinates when rain falls, this stage of its growth being known 

 as oidium. Its time of attack is when the leaves are expanding, 

 and, as the tree develops, the young shoots will be found to be 

 covered with the same kind of thing, and in addition black specks 

 will be seen studded over them. The object of this second kind 

 of fruit is to tide the fungus over the winter ; the leaves of the 

 tree perishing with the autumn, having done their work, the 

 fungus must be able to maintain its existence on the woody tissue. 

 Another kind of fruit, more complicated altogether, is the result 

 of fertilization. The spores contained in this kind will not always 

 germinate in the same way, varying according to the nature of the 

 food supplied by the plant on which they have been produced. 

 In the spring, when the rose-tree is beginning to expand its buds, 

 the temperature is just that which is required for the germination 

 of the spores, which then produce still smaller spores, like fine 

 powder. These are blown about by the wind and find places in 

 the opening leaf-buds of surrounding rose-trees, there repeating the 

 process. 



There are sent to Kew myriads of examples of such plant-diseases 

 every year, but there is no cure for the diseases when once established, 

 although they may be checked. "When the leaf-buds are beginning 

 to expand they should be syringed or sprayed, using a bottle 

 something like a hairdresser's, filled with Condy's fluid — mere 

 watering will not do. By using Condy's fluid, which can neither 

 kill nor hurt any plant, and spraying the trees once or twice 

 a week, all the fungi will be killed during the early development 

 of the leaves. If, however, the disease comes out as mildew it 

 shows that it has done its work, and that the injury has been done 

 inside the leaves, the so-called vegetative portion of the fungus 

 being inside the leaf ; and unless this stage were anticipated there 

 would be no chance of success in preventing the further develop- 

 ment of the disease. 



When geraniums are attacked by mildew I would recommend 

 spraying the plants in the conservatory, where myriads of germs 

 would be killed and no harm would be done. It may have been 

 noticed that geraniums which have been cut where they are 



