370 THE AMERICAN MONTHLY [Dec 



thai a cluster-cup, a rust, and a braud might be merely 

 succesisive stages of the same fungus, specific names had 

 been assigned to each of the forms, with the reHult tliat 

 some of these parasites have three names; and this in- 

 convenience is still unavoidable in cases where the con- 

 nection between the diflFerent stages hns not yet been 

 demonstrated. 



But what invests this group of fungi with peculiar in- 

 terest is tlie fact that many of them spend their first or 

 aecidium-bearing, stage on a different species of host- 

 plant from that which they inhabit at a later period of 

 their life history, when they develop uredo- and teluto- 

 sporee. Thus there are several kinds which produce 

 aecidia on the leaves of firs and pines, and then migrate 

 to jilants of the Heath order. To this changing of hosts 

 the name Heteroecism {Jietcr, "other" ; oikos, "house") 

 has been given. Analogous phenomena are observed 

 among animal parasites. The same organism which oc- 

 casions "measles" in pork, causes the tapeworm in man 

 while in the cat it is but a more advanced form of one 

 that inhabits the intestines of the mouse; and the liver 

 fluke of the sheep passes one part of the cycle of its de- 

 velopment in the body of a pond snail. Farmers long 

 suspected that the presence of berberry bushes in their 

 hedges had something to do with the rust that destroyed 

 their wheat. This idea was verified by the discovery 

 that Pucchlia graniinis is merely a later stage in the de- 

 velopment of JEcidiiun berbcridis which infests the ber- 

 berry. As the alternation of generations was first traced 

 in this species, it is the example of heter(pcism usually 

 iriven in text-books, but a similar connection has been 

 made out in many other inij-tances. The cluster-cups of 

 the Scotch fir belong to the same Uredine which bears 

 telato and uredospores on the groundsel; those of the 

 colts-foot correspond to telutospores on the meadow grass 

 of Puccinia poariun : yEcidium urtic<s of the nettle devel- 



