232 DISEASE IN PLANTS. 



liquid excretions more or less indicative of diseased 

 states are by no means confined to wounds or 

 definitely injured tissues, in which case such terms 

 are wholly misapplied. 



Honey-dew." ^The leaves, or other organs, of 

 many plants are sticky in hot weather, owing to 

 the excretion of a sweet liquid containing sugar, 

 the consistency and colour of which vary accord- 

 ing to circumstances. This honey-dew must not 

 be confounded with the normal viscidity of certain 

 insectivorous plants e.g. Sundew or with the 

 sticky secretion on the internodes of species of 

 Lychnis^ etc., where it plays the part of a protec- 

 tion against minute creeping things. 



Honey-dew is often met with on Lime trees, 

 Roses, Hops, etc. In many of these cases the 

 honey-dew is excreted by Aphides, which suck 

 the juices of the leaves and pour out the 

 saccharine liquid from their bodies. The sweet 

 fluid is in its turn sought after by ants, and 

 also serves as nutritive material for various 

 epiphytic fungi e.g. sooty mould, Capnodiiini, 

 Fuiiiago, and Antemiaria which give the leaves 

 and honey-dew a brown or black colour. Certain 

 Coccideae also excrete honey-dew, especially in 

 the tropics. 



At least one case is known where honey-dew is 

 formed as the result of the parasitic action of a 

 fungus, namely Claviceps purpurea in its conidial 

 stage on the stigmas of cereals, and this ma}' be 

 compared with the sweet odorous fluid excreted 

 by the spermogonia of certain Aecidia. In both 



