294 PROCEEDINGS OF THE 



devoured by another, till, as a happy consummation for them, they 

 are gulped into a ravenous maw where they find a congenial climate 

 and awake to new activities. The dog pleasurably gorges himself 

 with rabbit, but often worries up at the same time a sufficiency of 

 these included morsels to mar his future. In the same way the 

 best xnousers among cats are in danger of most misery. Cow, sheep, 

 and pig harbour parasites that produce various species of tapeworm 

 in man, when human wisdom — in the shape of boiling, roasting, 

 and the like — is at fault in thoroughness. The parasite ordinarily 

 assumes a different form in each of the animals which it inhabits ; 

 but sometimes all its metamorphoses are completed in the same 

 animal — as is the case with trichince — and then carried out de novo 

 in the next suitable flesh-eater in which it gains a settlement. 



I remind you of these facts, as my subject is one of a kindred 

 nature to which much attention has only been turned in recent 

 years, the heteroecism and dimorphism of certain vegetable parasites, 

 the Uredines, that infest the leaves, stems, flowers, and fruits of 

 plants. The conclusions of many competent observers have been 

 to the effect that some parasitic fungi can, for the furtherance of 

 their own interests, migrate from plant to plant and take different 

 forms if needful. Though a few able botanists are still disinclined 

 to admit that such heteroecism is clearly established, it seems to me 

 that its existence in many instances can hardly be doubted, though 

 many details still await confirmation or correction. The different 

 forms which these parasitic fungi assume at various stages have led 

 to their being referred to several distinct species, as iEcidium, 

 Uredo, Puccinia — a classification similar to what that of the larva, 

 pupa, and imago of an insect as distinct species would be. In any 

 fresh classification there arises the difficulty of settling which of 

 the names the species should bear ; and, as sexuality in these plants 

 has not yet been established, all nomenclature is in the meantime 

 provisional. In recent classifications the name given to the resting- 

 spore stage, as the most advanced yet known, is generally adopted. 

 Should it be established, however, that the cluster-cup stage is a 

 sexual generation, as has long been surmised and is highly probable, 

 this nomenclature would undergo extensive changes, as that condition 

 would then be recognised as the most complex, so that what is now, 

 for instance, generally called Puccinia would be termed iEcidium. 



A typical iEcidium, I may remind you, has mycelium that 

 ramifies in the interior leaf-tissue and produces on the under surface 



