Fungoid pests 



OF 



CULTIVATED PLANTS 



Introduction. 



Some introductory remarks are necessary as an explanation of the main 

 facts in the life-history of some of the principal parasites to be recorded, 

 and thus prevent their subsequent repetition when each species is under 

 consideration. Thus iteration will be avoided and space economised 

 where there is so little to spare. 



One of the most rudimentary lessons to be inculcated is the known 

 fact that parasitic fungi may be arranged under two types, each 

 with a different mode of development, and each requiring a different 

 mode of treatment. It is, at the least, essential to know to which of 

 these types any given pest belongs before effectual steps can be taken 

 against it. We have called these two groups the epiphytal and the 

 endophytal. The former includes those fungi which establish themselves 

 on the surface of the leaves, stems, or other green parts of living plants, 

 and ultimately cause destruction by a kind of suffocation, and not by 

 affecting, distorting, or absorbing the internal tissues. It is natural to 

 suppose that it is this type of fungus pest which is most amenable to the 

 application of fungicides, the object being to destroy the parasite without 

 injury to the host-plant. We may give as examples the hop mildew and 

 the oidium of the vine, both of which are to be kept in check by the 

 application of sulphur. In these cases a white mould is developed in 

 irregular blotches, or broad effused patches, over either or both surfaces of 

 the leaves, the inferior stratum consisting of delicate interwoven threads, 

 forming a mycelium, which attaches itself by means of haustoria, or 

 suckers. From this mycelium arise the short fertile threads, which are 

 mostly clavate. The upper portion is soon separated from the lower by 

 a septum, at which it is constricted, and this upper cell, of an elliptical 

 shape, becomes a conidium. Whilst this process is going on another 

 septum is developed at an equal distance below the first, and another 



B 



