4 FUNGOID PESTS OF CULTIVATED PLANTS 



conidia must be destroyed in the autumn to prevent their extension to 

 healthy plants ; and the destruction of all rotting debris must be carried 

 out during the winter, so as to extirpate all the concealed resting spores, 

 and thus prevent the infection of seedlings in the spring. 



From these details it will be evident that plants once attacked by 

 cndophytal parasites are in themselves hopeless. No external application 

 can destroy organisms which it cannot reach, or, if they could be 

 destroyed, no manipulation can replace the disorganised tissues. Hence, 

 then, all efforts should be directed towards the destruction of the conidia 

 and resting spores, in order to stamp out the disease at its source and 

 prevent the future infection of healthy plants. The application of spray- 

 ing to plants apparently without disease would be done as a preventive, 

 in order to destroy at once any germs which might be brought into con- 

 tact with the foliage ; and the destruction of all infected material would 

 limit the local sources of infection. With an intelligent appreciation of 

 the objects which have to be attained, the cultivator may accomplish a 

 great deal in the way of prevention, even though he may be helpless to 

 effect a cure. It will be seen how much of this depends upon an accurate 

 diagnosis of the disease. 



There are many other forms of endophytal parasites, and the life-history 

 of some of these is still obscure. In the majority of them only a conidial 

 fructification is yet known, and the internal tissues do not appear to be 

 so absorbed and destroyed as in the case of the "rot moulds " ; but in 

 such black moulds as the " Apple and Pear scab " the mycelium appears 

 to be perennial, and produces a fresh crop of conidia each successive year. 

 There is some evidence that this disease is deep-seated and hereditary, 

 and if so it is doubtful whether any amount of external application will 

 result in a perfect cure. The genus Glceosporium includes many species 

 which are very destructive, but often they seem to be localised, and the 

 mycelium may not pass internally to other parts. This can only be 

 ascertained by closer investigation. The little pustules on the leaves, and 

 the fruits, are seated beneath the cuticle, where- a cushion or stroma of 

 compacted mycelium produces conidia, but without any enclosing mem- 

 brane or perithecium. When the conidia are matured the cuticle is 

 ruptured, and the spores escape to the surface, in many cases adhering in 

 a somewhat gelatinous mass, which oozes out in the form of tendrils. In 

 such cases it is evident that the application of some fungicide capable of 

 destroying the vitality of the conidia will be of service in preventing the 

 spread of the disease (PI. 1, fig. 9). 



A large and important group of endophytes is that known as the 

 Uredines, of which the common and disastrous " Wheat rust " or " Wheat 

 mildew " is a familiar example. In the first instance, the host-plant pro- 

 duces upon its leaves, in the spring, clusters of little cups, partly embedded 

 in the substance of the leaf, which is usually thickened and discoloured. 

 These little cups constitute the "cluster cups," or aecidium form; the 

 margin is usually white and fringed, and the interior filled with orange 

 subglobose spores, termed aecidiospores, produced in chains, but soon 

 falling apart (PL I. fig. 21 ). The aecidiospores will germinate when mature 

 and produce a thread of mycelium, which is capable also of producing 

 secondary spores (fig. 1). Smaller bodies are also to be found in company, 



