388 DIVISION III-—MODE OF LIFE OF THE FUNGI. 
uredospores and teleutospores on Gramineae; Uromyces Pisi forms uredospores 
and teleutospores on Vicieae and its aecidia 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 Juniperus, 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 Géppertiana, 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 Peridermium Pini. The rest of the known cases of the kind will be found 
collected together in Winter’s Pilzfiora. 
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 Peri- 
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 /foxeny 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 thallus 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 Claviceps 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 Curreyana 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 Ascomycetes which inhabit leaves, such as Polystigma, Rhytisma, Phyllachora, 
