_Flux._--It is a common event to see fluids of various kinds issuing from wounds in trees, or congealing in more or less solid masses about them; and owing to the prevailing tendency to compare plant diseases with those of animals, we find such expressions as _Gangrene_, _Ulcer_, and so forth, applied to these "open sores." In so far as such outflowings frequently indicate diseased states of injured tissues which are incapable of healing up, the analogy is perhaps a true one; but it must be remembered that very different structures and processes in detail are concerned. Moreover, 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 according 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 protection 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, _Capnodium_, _Fumago_, and _Antennaria_--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 may be compared with the sweet odorous fluid excreted by the spermogonia of certain _Aecidia_. In both cases the sweet fluid attracts insects which disperse the spores. Honey-dew may also be formed without the agency of fungi or insects, when hot and dry days are followed by cool nights, with a saturated atmosphere, _e.g._ _Caesalpinia_, _Calliandra_ and other trees in the tropics, which are called rain trees owing to the numerous drops of fluid which drip from the leaves under the abnormally turgescent conditions referred to. _Cuckoo-spit._--The leaves of Willows, Meadow grasses and herbs, etc., are often seen with froth on them, in which is a green insect, _Aphrophora_, which sucks the juices from the tissues and excretes the frothy watery cuckoo-spit from its body.