388 DIVISION 111. — MODE OF LIFE OF THE FUNG J. 



uredospores and telcutospores on Gramineae ; Uromyces Pisi forms uredosporcs 

 and teleutosporcs on Vicieae and its accidia on Euphorbia Cyparissias, the well-known 

 Euphorbia-aecidium. Next to these species all the Gymnosporangieae are examples 

 of the phenomenon in question, as Oersted was the first to show from gardeners' 

 traditions; their teleutospore-layers inhabit species of Junipcrus, and migrate to Pyrus 

 and other Pomaceae for the formation of aecidia, which were once known by the 

 name of Roestelia. The aecidia of several species which live on the Ericaceae are 

 formed on leaves of the Abietineae which are entering their first year, those of 

 Melampsora Goppertiana, as Hartig showed, on Abies pectinata ; those of Chrysomyxa 

 Rhododendri, the Fungus of the alpine rose, and of C. Ledi on the spruce, Abies 

 excelsa. The Coleosporium of species of Senecio migrates according to Wolff to the 

 leaves of Pinus sylvestris, and there produces its aecidia which were known by the old 

 name of Pcridermium Pini. The rest of the known cases of the kind will be found 

 collected together in Winter's Pilzflora. 



The same work also enumerates the forms bearing teleutospores and those 

 bearing aecidia, of which it is known that the germs which are capable of infecting do 

 not proceed to further development on the hosts on which the forms themselves 

 grew. The aecidia-forms never propagate themselves on their hosts ; teleutospore- 

 forms are produced only in certain circumstances through the medium of the 

 uredospores which accompany the teleutospores. From the analogy of the cases in 

 which metoecism is certainly known these forms must be separate sections in the 

 development of metoecious species. Their complete form-cycle has yet to be 

 ascertained. To this group belong on the one hand most of the species of Melam- 

 psora and Coleosporium, the Cronartieae and also Hemileia vastatrix, the Fungus of 

 the coffee-plant, on the other the aecidia of fir-cones, the aecidium known as Pcri- 

 dermium elatinum which causes the ' witches' brooms ' in Abies pectinata (see 

 page 368), the aecidium of species of Clematis, and many others. 



Metoecism, that is, enforced change of the living host, is not known outside the 

 group of the Uredineae ; its supposed occurrence in other species has not yet been 

 confirmed. There is another phenomenon which must of course be kept quite distinct 

 from it, and which may be termed lipoxeny or deserting the host in opposition to 

 a change of the host. Many Fungi which inhabit plants spend a certain period of 

 their life in strictly parasitical fashion on the host, and then separate from it and 

 complete the other sections of their development independently without a living host, 

 and entirely at the expense of the reserve of food which they have appropriated from 

 the host. The separated lhallus may be compared as regards the economy of the 

 metabolism to a ripe spore which is able to germinate at the expense of the reserve of 

 food which it contains. This phenomenon is most striking in Claviccps which 

 continues strictly parasitic up to the ripening of its sclerotia, and produces the stromata 

 from them after they have fallen from the plant under favourable conditions of temper- 

 ature and supply of water in the next period of vegetation (see on page 227). A similar 

 course of events may take place in Peziza Durieuana which forms its sclerotia 

 on stems of Carex, and Peziza Currevana which forms them on stems of Juncus 

 and Scirpus, and produces ascocarps from them in the next period of vege- 

 tation. The Sclerotinieae may also be mentioned in this connection ; and the long 

 series of Ascomycetcs which inhabit leaves, such as Polystigma, Rhytisma, Phyllachora, 



